His father had the same quirk the ability to steal the quirks of others and use them himself.
Combining similar quirks together for more powerful effects.
Caused his father to become the world's greatest villain.
But like all humans he aged. Though slowed by a longevity quirk.
He needed an heir someone worthy of his quirk and his title of the world's greatest villain. So the man attempted many times to sire a child with the quirk. The man tried 18 times to produce a child with the same quirk as him.
And he failed 17 times.
Some of the children had their mother's quirks. Others had copies of his stolen quirks. As well as useless quirkless failures. Though one had the ability to temporarily copy the quirks of others but it was irrelevant compared to the power of his own.
But the 18th his favorite had his quirk. Not only that but his quirk was active at birth stealing his mother's quirk in childbirth killing her or so the story he told him went.
The father trained the boy but it was like torture for the boy.
But his quirk had a unique side effect. Taking people's quirks their greatness, their power was like a drug to him.
One day the boy escaped his father's powerful grasp. Stealing quirks to feed his addiction the boy ruined many lives. But through it all he wished to become a hero as great as All Might.
He one day he encountered the great hero who showed the boy a way to greatness.
To redeem his name and his quirk from his father's dark legacy.