Marvolo Gaunt

Marvolo Gaunt was a Pureblood wizard and the maternal grandfather of Lord Volemort, the main antagonist of the Harry Potter series. A racist, villainous man, he was a fervent believer in Pureblood supremacy and believed he was above the law because of his relation to Salazar Slytherin (though it is unknown if he ever went to Hogwarts).

History
Marvolo Gaunt was born somewhere between 1850 and 1880. According to Albus Dumbledore, the Gaunt family's taste for extravagance left them impoverished long before Marvolo was born, and thus he lived in squalor, though he possessed two priceless heirlooms: Salazar Slytherin's Locket and Cadmus Peverell's Ring, both of which would later become Lord Voldemort's Horcruxes. Due to generations of inbreeding in his family, Marvolo had several mental and physical problems from the day he was born, and his heritage--including his ability to talk to snakes---made him extremely arrogant, violent, and prideful. He lived in a dirty shack in Little Hangleton, England for his entire life.

At some point, Marvolo married (it is unknown if his wife died later or left him due to his behavior) and fathered two children, Morfin and Merope. Marvolo was a terrible father, viciously abusing his daughter to the point of unintentionally suppressing her ability to use magic and treating her like a slave, while he got along rather well with Morfin, who shared his father's arrogance, pride, and penchant towards violence.

At some point, Morfin attacked the rich Muggle Tom Riddle, an act that Marvolo approved of. The Ministry of Magic sent Bob Ogden, an Auror, to investigate the incident and inform Morfin that he would have to attend a hearing for his actions. Marvolo showed no respect for Ogden and maliciously flaunted his "superior bloodline", though his bragging failed to intimidate the Auror. When Morfin eagerly informed his father that Merope was in love with Tom Riddle, Marvolo flew into a rage and tried to strangle her, but Ogden quickly stopped him. Marvolo and Morfin attacked Ogden, who escaped and returned soon after with reinforcements and arrested the duo after a brief skirmish. Marvolo was sentenced to six months in Azkaban, while Morfin's sentence was three years.

Now safe from her wicked brother and father, Merope enchanted Tom Riddle (likely with a Love Potion) and eloped with him. Marvolo, unaware of this, served his prison sentence and returned to the shack, arrogantly and foolishly expecting his daughter to have awaited his return with a hot meal on his table. Instead, he found the shack empty except for a letter from Merope, explaining what she had done. Shocked by this, Marvolo never mentioned her again and died soon after this. Possible reasons for his early death are that Azkaban greatly weakened him and/or that he just never learned to feed himself.

Legacy
Years after his death, Marvolo's ring was stolen by his grandson, Tom Marvolo Riddle (later Lord Voldemort), who turned it into a Horcrux.

Appearance
Marvolo Gaunt was a short man with rather long arms. He is described by Harry Potter as resembling an aged, yet powerful monkey, not unlike his ancestor, Salazar Slytherin.

Personality
Due to genetics and his upbringing, Marvolo Gaunt was a violent, arrogant man who placed the importance of his heritage above everything else. He hated his daughter, Merope, and treated her like a slave, while getting along with his son, Morfin, who shared his supremacist beliefs and violent behavior. He also had no respect for the law or authority, particularly when it involved Muggles, believing that his son had committed no crime by attacking Tom Riddle and speaking condescendingly towards Bob Ogden.

He was prone to fits of brutal violence when he heard or saw something he didn't like, such as beating his daughter viciously when she dropped the pots and pans she was using to cook food and trying to kill her when he learned she was in love with a Muggle. He greatly cherished his family heirlooms, and cherished his son just as much, according to Dumbledore. Despite his abusive behavior, he  believed that Merope was loyal to him, as evidenced by his foolish expectation that she would remain at the shack with a hot meal ready on his table when he returned from Azkaban, and was utterly shocked when he learned that she had run off with Tom Riddle.