Regulus Black died in 1979. He was killed por the inferi while he was on his quest to receive Voldemorts locket horcrux and later see it destroyed. He was only 18 years old.

Regulus was part of the Black Family, which was almost all Slytherins. They believed in blood-purity. Regulus did too, in the beginning of his life, although he was Sirius' younger brother. We know Regulus was interested in Lord Voldemort, because in the Deathly Hallows when the trio buscar his room for Voldemorts locket, they find newspaper clippings all around his room that were about Voldemort. In the beginning of his life, he took after his family in every way.

However, something changed Regulus' vistas on Voldemort, when he hadn't even been a Death Eater for that long. One of the reasons being that Voldemort had harmed the Blacks house-elf Kreacher while he set up the security for his horcrux. It is also believed that Regulus did not like the means Voldemort was using to reach his goals.

After realizing all of this, Regulus had to do something about it. He knew of the horcruxes, and of ones location, so he set out with Kreacher to receive and destroy it. Regulus drank the potion por himself, and sent Kreacher inicial with orders to destroy the locket. He later drowned in his attempt to get water from the lake, because the inferi pulled him under.

It is unfortunate, and sad, that until Kreacher told the story of his master, no one knew. Sirius was under the impression that Voldemort had him killed because Regulus was scared of doing a mission of some sort. Most likely, that is what everyone thought. But that isn't what happened. He died in a quest to make Voldemort mortal someday. He died valiantly, at only 18 years of age. Regulus Black should be remembered as the unsung hero.