Regulus Phineas Black I (1906-1959) was the youngest child of Sirius Black II and Hesper Gamp. He was a infamous potion smuggler at the time of his death in 1959. He was also the younger brother of Arcturus and Lycoris.
Regulus was a thin and sinister looking wizard with great beauty but distant none the less.
Regulus was a closed and private person that was very different from his father.
Regulus attended Hogwarts from 1917 to 1923 and was sorted into Slytherin House. In 1959, he was caught in a group of Potion smugglers retrieving illegal veritaserum and love potions on the docks of London. He was killed by an Auror. This incident greatly affected the reputation of his uncle and auror Arcturus Black II. In 1961, his great-nephew was named after him.