CANON
Regulus Arcturus Black was one of the two Black children; the son of Orion and Walburga Black and younger sibling to Sirius Black. He was born in 1961 - one year after Sirius. He was named after both his great-uncle and his paternal grandfather - Regulus Black and Arcturus Black, respectively.
Where Sirius rebelled from the norm in the Black family, Regulus conformed nicely - following the family values of pure-blood superiority to a T and being sorted into Slytherin. Once Sirius was disowned, Regulus would become the sole heir of the House of Black. In school he was a good, if quiet student - a seeker for the Slytherin quidditch team and a year behind his brother (whom he would studiously ignore whenever possible, preferring not to associate with him). As for friends, he kept to Slytherin - a notable aquaintance and friend being one Severus Snape, who he met under circumstances that were perhaps not the best. Both being Death Eaters so young, it was a given that they would end up spending time together - and thus their friendship of sorts - however twitchy or rough around the edges it may have been - grew.
While Regulus' parents never joined the Death Eaters themselves, they were overjoyed that their favorite son, their heir, held so strongly to their beliefs that he would join the Dark Lord's forces. However, Regulus was not as steadfast in these beliefs as his parents - at some point after taking the dark mark, he began to question the Dark Lord and his methods and purposes. (While it is possible that one of these reasons for questioning him being that Regulus found out about his half-blood status, other factors point to different reasonings.) One of the events - truly, the last straw it seems - was when Voldemort caused harm to his loyal house elf Kreacher - leaving him to die with the Inferi after hiding one of the Horcruxes. Kreacher managed to return to Regulus and relay the events, which caused Regulus' final decision to defect. Knowing now what the locket really was based on Kreacher's story and Voldemort's own boasting, he ordered Kreacher to take him to the underground lake.
Once there, Regulus drank all of the potion concealing the locket and, having Kreacher switch the horcrux with a fake one containing a note that was all but a slap in a face to his formerly beloved Dark Lord, ordered him to return home and destroy it - submitting himself to the death that he knew was coming with the Inferi - welcoming death for having given the world a larger chance at defeating Voldemort. He ordered the elf to tell no one anything - knowing that he would not be able to disobey. Without knowing until it was too late who ruined his plans, Voldemort would not come after his family.
Where Sirius rebelled from the norm in the Black family, Regulus conformed nicely - following the family values of pure-blood superiority to a T and being sorted into Slytherin. Once Sirius was disowned, Regulus would become the sole heir of the House of Black. In school he was a good, if quiet student - a seeker for the Slytherin quidditch team and a year behind his brother (whom he would studiously ignore whenever possible, preferring not to associate with him). As for friends, he kept to Slytherin - a notable aquaintance and friend being one Severus Snape, who he met under circumstances that were perhaps not the best. Both being Death Eaters so young, it was a given that they would end up spending time together - and thus their friendship of sorts - however twitchy or rough around the edges it may have been - grew.
While Regulus' parents never joined the Death Eaters themselves, they were overjoyed that their favorite son, their heir, held so strongly to their beliefs that he would join the Dark Lord's forces. However, Regulus was not as steadfast in these beliefs as his parents - at some point after taking the dark mark, he began to question the Dark Lord and his methods and purposes. (While it is possible that one of these reasons for questioning him being that Regulus found out about his half-blood status, other factors point to different reasonings.) One of the events - truly, the last straw it seems - was when Voldemort caused harm to his loyal house elf Kreacher - leaving him to die with the Inferi after hiding one of the Horcruxes. Kreacher managed to return to Regulus and relay the events, which caused Regulus' final decision to defect. Knowing now what the locket really was based on Kreacher's story and Voldemort's own boasting, he ordered Kreacher to take him to the underground lake.
Once there, Regulus drank all of the potion concealing the locket and, having Kreacher switch the horcrux with a fake one containing a note that was all but a slap in a face to his formerly beloved Dark Lord, ordered him to return home and destroy it - submitting himself to the death that he knew was coming with the Inferi - welcoming death for having given the world a larger chance at defeating Voldemort. He ordered the elf to tell no one anything - knowing that he would not be able to disobey. Without knowing until it was too late who ruined his plans, Voldemort would not come after his family.