Thundercat

Raised in Compton and other parts of Los Angeles, Bruner was born into a family of musicians, including his father Ronald Bruner Sr., a drummer, and his mother Pam, a flautist and percussionist. His father played drums for the Temptations, the Supremes, and Gladys Knight, amongst others. After Bruner Sr. got sober from cocaine, the children would watch him play gigs at the Crenshaw Christian Center. Bruner attended Locke High School, playing in the school's jazz band. His teacher, Reggie Andrews, produced and co-wrote the Dazz Band's 1982 single "Let It Whip" and collaborated with Rick James. Andrews re-introduced Bruner to Kamasi Washington; the two had originally met as children, through their fathers' membership in a gospel fusion band. The reunited duo would sneak into jazz concerts, driving around in a worn-down 1982 Ford Mustang to do so. They would later get to play the same venues as the performers they watched. They also did sessions with Bruner's cousin Terrace Martin in Washington's father's garage during this time.

He has a daughter named Sanaa. Other members of Stephen's musician family include Stephen's youngest brother, Jameel Bruner who was a keyboardist in Odd Future's neo-soul/jazz group The Internet on their 2015 album Ego Death alongside guitarist Steve Lacy, who was making his debut at that time. Bruner was a close friend of the rapper Mac Miller, and the two often spent time together in their personal lives. Miller's death in 2018 made Bruner confront his own substance use and alcoholism, causing him to drink less and adopt better eating habits, including becoming vegan. "It's sex, drugs and rock'n'roll. It's real. You ride the line, you don't know how close you are sometimes. Do I think he meant to die? No, I don't think he did. Even though that sometimes creeps in there because you're always on the edge of a knife. Sometimes you mess up. That happens a lot," Bruner shared in a 2020 interview with The Guardian. Bruner is a big fan of anime and cartoons, and often wears outfits and accessories that reflect this, such as a Pikachu backpack, cat-ear headbands, and the Interface Headset from the anime Neon Genesis Evangelion. His stage name, taken from the 1985 cartoon series Thundercats, is further evidence of these influences. Bruner is a Christian, and incorporates many of the religion's themes in his music.