Sirius was the last heir of the House of Black, a once notable pure-blood wizarding family. His parents, Orion and Walburga Black, were both Blacks by birth and second cousins. Sirius had a younger brother, Regulus, who lived 1961-1979."Sirius" is a traditional Black family name, recurring in at least three generations and following a family tradition of naming children after stars, constellations and galaxies. The names Cygnus, Arcturus, and Regulus have also occurred at least twice each. Notably, however, only one Sirius (the subject's great-grandfather) left a line of descent, which ended with the youngest Sirius. During his childhood, Sirius had a large family: four grandparents (Arcturus, Melania (nee Macmillan), Pollux and Irma (nee Crabbe) Black), two maternal uncles (Alphard and Cygnus Black) and one paternal aunt, Lucretia Prewett (nee Black). Cygnus's wife Druella Black (nee Rosier) was his aunt by marriage, and Lucretia's husband Ignatius Prewett was his uncle by marriage. He also had three older cousins, Bellatrix Black (whom he detested, and who would eventually kill him), Andromeda Black (his favourite cousin and mother of Nymphadora Tonks), and Narcissa Black (Mother of Draco Malfoy, whom Sirius also disliked). The pure-blood Black family believed strongly in pure-blood elitism. They refused to consort with Muggles (even Squib family members, such as Sirius's great uncle Marius were shunned) and insisted that their members only marry within respectable pure-blood classes; they also held the Dark Arts in reverence. Sirius rejected these values, leading to conflict with his family. When his cousins Bellatrix and Narcissa made desirable Pureblood marriages, to Rodolphus Lestrange and Lucius Malfoy respectively, Sirius held them in contempt. His favourite cousin, Andromeda, was disowned by the family as a "blood traitor" when she married Ted Tonks, a Muggle-born. Sirius would later share this designation. More distantly, Sirius was related to the Weasley, Crouch, Longbottom, and Crabbe families, among others. His great-aunt, Dorea Black, married Charlus Potter; it is unknown if Potter was related to the Potter family with whom Sirius would later become deeply involved. At Hogwarts, Sirius became best friends with James Potter, Harry Potter's father. These two also became friends with Remus Lupin and Peter Pettigrew. In the seventh book, it was revealed that Sirius also exchanged correspondence with Lily Evans, and it is known he did care for her - as shown by his rage after their deaths, when he says he would have died to protect them.
By the end of his life, Sirius had established other friendships: Harry, whom he loved as a son, Harry's friends Hermione and Ron, his distant cousins the Weasley family, and his first cousin once removed Nymphadora.Sirius's early life proved unhappy; by adolescence he had come to hate most of his relatives, in particular his mother and his cousin Bellatrix. He rejected his family's pure-blood elitism, reverence for the Dark Arts, and their insistence on respectable pure-blood marriages. "I ran away from home...I'd had enough...[Why did I] leave?...Because I hated the whole lot of them...I don't like being back here...I never thought I'd be stuck in this house again." Whereas all other members of the Black family were sorted into Slytherin house, Sirius was placed in Gryffindor, showing that his views had already diverged from those of the rest of the family before he came to school. By contrast, he greatly enjoyed life at Hogwarts, where he was inseparable from his best friend, James. Although he later considered himself "an idiot" during this time, he, along with James, was immensely popular: teachers respected his intelligence, though not his behavior; students liked his biting humour (which to a certain extent he shared with James, and later, Harry), and he was considered extremely handsome. He was very popular among girls. Many teachers regarded him and James as troublemakers or practical jokers; Hagrid compared them to the Weasley twins, and McGonagall also commented on the pair of troublemakers. His popularity was not universal, however. Early on, a mutual hatred sprang up between James and Severus Snape. Sirius actively supported James, leading to Snape bestowing an equal and life-long loathing upon Sirius. Sirius hated Snape because he was "this little oddball who was up to his eyes in the Dark Arts" - James detested the Dark Arts and those who practised them. Sirius and James often went out of their way to bully Snape. While watching one of Snape's memories in the pensieve, Harry sees Sirius and James attack him only because they were bored. Sirius attempted to justify this by insisting Snape had a mean streak and was not the innocent victim the memory depicted him as. Sirius also suggests that Snape envied James for his popularity and talent.
Sirius and James also became friends with another student, Remus Lupin, whom they later discovered was a werewolf. To support Lupin, Sirius, James, and another friend, Peter Pettigrew, secretly (and illegally) became Animagi, which allowed them to safely accompany Remus during his transformations and keep him under control. The four friends roamed Hogwarts's grounds during the full moon. After mastering animagery, Sirius's form took the shape of a huge black dog, from which his nickname "Padfoot" was derived.Late in his Hogwarts career, the feud between Snape and Sirius reached its climax when Sirius told Snape how to enter the tunnel leading to the Shrieking Shack where, unbeknownst to Snape, Lupin was confined during his transformations. Sirius sent him there during a full moon, expecting that Snape would meet the transformed werewolf - a potentially deadly trick that could have killed Snape. James was forced to rescue him. Sirius excused his own actions, explaining that he had simply told Snape what he wanted to know (about the tunnel) whilst omitting crucial information (that it led to a deadly werewolf); he also claimed it "served Snape right". After leaving school, Sirius fought against Voldemort, eventually joining The Order of the Phoenix. He remained friends with James Potter, eventually attending James and Lily's wedding as Best Man. When their son, Harry, was born, James and Lily named Sirius godfather, thus designating him as Harry's guardian in the event of their deaths. He also gave Harry his first broom at the age of one as a birthday present, as stated by Lily in a letter.
In 1981, the Potters were aware that their son - and the son of Frank and Alice Longbottom, two other Order members - were Lord Voldemort's specific targets. Albus Dumbledore advised the Potters to go into hiding using the Fidelius Charm, a highly complex spell allowing a Secret to be concealed within another person (the "Secret Keeper"). James and Lily wanted Sirius to be their Secret Keeper. However, believing Voldemort would suspect him but not a "weak, talentless thing" like Peter Pettigrew, Sirius and the Potters reassigned Pettigrew to this role. No one, not even Lupin or Dumbledore, knew this.On Halloween night 1981, Sirius went to Pettigrew's hiding place and found him missing: he later discovered that Pettigrew betrayed James and Lily by revealing their secret whereabouts in Godric's Hollow to Voldemort. Sirius frantically sped to James and Lily's home, discovering the house destroyed and his friends dead; only baby Harry was still alive. Sirius tracked down Pettigrew, determined to kill him in vengeance. However, Pettigrew outwitted Black: confronted by Sirius on a city street, he blew it up, faking his own death (leaving a severed finger behind as evidence) and killing 12 Muggles in the process. Sirius was arrested by the Department of Magical Law Enforcement, accused of murdering his three friends, serving Lord Voldemort, and killing the Muggles. He was sentenced without trial to life imprisonment in Azkaban Prison by the Head of the Department of Magical Law Enforcement, Barty Crouch Sr. He spent the next 12 years in solitary confinement at the mercy of the Azkaban guards, the Dementors. Driven to the brink of madness, he retained his sanity by focusing on his innocence - a thought not cheerful enough to be detected by the Dementors, but which gave him small comfort. However, his brooding over his friends' deaths and Pettigrew's betrayal became an obsession. In Harry Potter and the Prisoner of Azkaban, Sirius was able to keep his sanity by knowing his innocence. When he found out that Pettigrew was using his animagus form to become a pet to a boy at Hogwarts (Ron Weasley), he realised that Peter would easily be able to deliver Harry to Voldemort if he ever regained power. This resulting obsession cleared his mind and gave him the mental strength to escape Azkaban. He is the first person known to have escaped the wizard prison, accomplishing this feat by transforming into his Animagus dog form. The dementors' inability to perceive unsophisticated canine minds, along with his severe weight loss from malnutrition, allowed him to slip through the cell's bars. After his escape, Sirius takes refuge in and around Hogsmeade, intent on exacting revenge upon Pettigrew, who is disguised as Ron Weasley's pet rat, Scabbers, but also to look after Harry. During this time as a dog, he also met Hermione Granger's cat Crookshanks, who had recognised that Sirius wasn't actually a dog, and who had also recognised what Peter was. Half-crazed and desperate, he on one occasion slashes the Fat Lady's portrait with a knife; on another, he is able to enter the Gryffindor common room (with help from Crookshanks, who had obtained the passwords for him) and shreds Ron Weasley's bed curtains searching for Scabbers. Although Sirius deeply cares about his godson, Harry believes Black betrayed his parents and vows to kill him. Towards the end of the novel, however, it briefly appears Black will be exonerated. Although Harry nearly kills him, Lupin's timely intervention saves Sirius. Lupin, who now knows Sirius is innocent, is reunited with Black; Pettigrew is unmasked; and, most importantly, Harry prevents Black and Lupin from murdering Pettigrew. Harry begins to view Sirius as a surrogate father, although events swiftly turn against him again - Pettigrew escapes, and Sirius is captured by the Dementors at Hogwarts and sentenced to "The Dementor's Kiss", a fate worse than death; the Kiss will suck out a person's soul, yet still leave them alive as an empty shell of living death. Harry and Hermione help him escape with Buckbeak, a hippogriff who has also been unjustly condemned. Black is once again a wanted man. Following the events of Prisoner of Azkaban, Sirius flees Europe - to somewhere tropical, Harry believes - beyond the Ministry of Magic's jurisdiction. There, he slowly recovers from his years in Azkaban. Although he can only communicate sparingly with Harry by owl post, he gives reasoned and sensible advice. Harry grows closer to Sirius and relies on his help. A worried Sirius returns to Britain during Harry Potter and the Goblet of Fire, when Harry's scar begins hurting him again (a signal of Lord Voldemort's presence or power), coupled with reports of the Death Eater activities at the Quidditch World Cup. He sacrifices some of his regained health to help Harry: by the time he reaches Hogsmeade, he is once again gaunt and dishevelled, hiding in a cave and surviving mainly on rats (with occasional food gifts from Harry and his friends). He has little influence on Harry in this book - his presence cannot prevent the disaster at the Triwizard Tournament, and he mostly dispenses advice and comforts Harry following Voldemort's resurrection. In Harry Potter and the Order of the Phoenix, Sirius takes refuge in his ancient family home at 12, Grimmauld Place in London. As the last Black, Sirius inherited the property and allows it to be used as the Order of the Phoenix headquarters, although it has fallen into disrepair. Magic hides its location. Due to the ongoing manhunt, Sirius is effectively confined there, even though Order member Kingsley Shacklebolt, who is a Ministry Auror and is in charge of the hunt for Sirius, knows Sirius is innocent. However, due to the Ministry of Magic's anti-Dumbledore stance and because Peter Pettigrew has informed Voldemort of Sirius's dog disguise, it is too dangerous for him to be in public. His confinement causes depression, and he is frequently withdrawn and antagonistic - especially so by Severus Snape's increasingly important role within the Order. The hostility between himself and Kreacher, his demented house-elf (who blames Sirius for the suffering he caused his mother, Walburga, whom Kreacher revered) also affects him. When he briefly leaves the house to see Harry, Ron, and Hermione off to Hogwarts, his Animagus form is recognised by Draco and Lucius Malfoy, resulting in more threats and warnings. Harry and Sirius stay in touch through owls and the Floo Network, a system to communicate through fireplaces. Sirius is nearly captured by Dolores Umbridge, a ministry official who was monitoring the Network and the owl mail in and out of Hogwarts. Despite his limited mobility, Sirius remains determined to help expose Voldemort and protect Harry, and he is ready to fight whenever needed.
Sirius acts as a father/older brother figure to Harry throughout the fifth book. Fun-loving, bold, and reckless, he encourages Harry to oppose Professor Umbridge and her reforms and strongly approves of Harry starting the secret Defensive tutorial group for students. He also demonstrates a high-level of trust in and respect for Harry, willingly answering the latter's questions about the Order of the Phoenix and Voldemort. Lupin and other characters (such as Molly Weasley, Ron's mother) express disapproval for Sirius's behaviour around Harry, saying that Sirius behaves with Harry as he did with James, Harry's father, and that this is inappropriate.With his growing power, Voldemort implants a false vision into Harry's mind that Sirius is captive at the Department of Mysteries. Convinced that Sirius is being tortured, Harry, along with Ron, Hermione and three other students (Ginny Weasley, Neville Longbottom and Luna Lovegood), fly to London on Thestrals. They enter the deserted Ministry of Magic and gain access to the Department of Mysteries. When they're ambushed by Death Eaters, Harry realises Voldemort lured him into a trap, and he and his friends are plunged into a desperate fight for survival. It is Snape who saves them; he alerts the Order that the students are missing and have probably gone to rescue Sirius (whom Snape already knows is safe). The Order immediately sends a rescue team; amongst them is Sirius. The Order battles the Death Eaters in "the Death Room". During a frenzied duel with his hated cousin Bellatrix he taunts her for failing to harm him. It is notable that in the film, Sirius mistakenly refers to Harry as James during this fight, a slip of the tongue that does not occur in the book. Bellatrix strikes Sirius with a curse, sending him backwards into the veil and to his death. Harry tries - and fails - to get revenge on Bellatrix, only to be interrupted by Lord Voldemort's arrival. After a short battle between Voldemort and Dumbledore, Voldemort flees, but not before being seen by the Minister for Magic and other ministry officials. As a result, the Ministry abandons its stance that Voldemort has not returned, and Albus Dumbledore is trusted once more. He, in turn, persuades the Minister that Black is innocent. By the following book, Black is exonerated; unfortunately for Sirius, it is far too late. Harry is left to mourn Sirius, reflecting that, despite his flaws, he was a loving and protective godfather, and the closest thing he had to a real father. As stated by JK Rowling during the BBC Paxman interview, 2003, Sirius Black is "definitely dead." She has created further intrigue, however, by making a cryptic reference to the communication mirror Sirius gave to Harry before he died: "The mirror might not have helped as much as you think, but on the other hand, will help more than you think. You'll have to read the final book to understand that!" In the final book, Aberforth Dumbledore uses the two-way mirror - which he bought from Mundungus Fletcher a year prior - to see Harry in the Malfoy cellars, which enables Aberforth to send Dobby to rescue Harry. Sirius makes his final appearance in the final book Harry Potter and the Deathly Hallows when Harry discovers the Resurrection Stone within the golden snitch. Appearing as a ghostlike figure alongside James, Lily, and Lupin, Sirius supports Harry's walk into death and assures him that dying is "quicker and easier than falling asleep". He also promises Harry that the four will remain a part of him. In light of his adventures and dangerous missions, Harry wonders if he'll be as reckless a godfather to Teddy Lupin as Sirius had been to him. The epilogue shows that Harry indeed forms a solid relationship with Teddy. *This information was taken from the Wikipedia.org website.