Greg K. is one of the founding members of The Offspring alongside singer Dexter Holland. Prior to forming The Offspring, he was also on the track and field team at Pacifica High School, along with bandmate Holland, where he took up playing the bass guitar. Greg K. and Holland had been playing locally since the early 1980s and formed Manic Subsidal in 1983. After hiring Noodles as their new Guitarist, Manic Subsidal changed their name to The Offspring in 1986. he attended Cal State Long Beach.
Greg K. graduated from Pacifica High School in 1983. He has been married to his wife Jane since 1998 and is a father of four sons, Michael, Matthew, Nolan, and Nathan. They currently live in the Huntington Harbour community in Huntington Beach, California.
On May 28, 2008, Greg K. announced on The Offspring's website that he was taking a hiatus from touring because of a "scheduled family matter" but would be returning to the fold by mid-June. Face to Face Bassist Scott Shiflett filled in for him on those shows. The "scheduled family matter" turned out to be a new child, as he became a father for the fourth time.