Jason Matthew Thirsk (December 25, 1967 – July 29, 1996) was an American musician who was the bass player of the California punk rock band Pennywise from 1988 through his death in 1996.

Pennywise was formed in 1988 by Thirsk along with singer Jim Lindberg, guitarist Fletcher Dragge, and drummer Byron McMackin.

[2][3] The band decided to continue making music after Thirsk's death, first by dedicating their performances to him at Warped Tour 1996.

One of Pennywise's most popular songs, "Bro Hymn", was originally written by Thirsk as a tribute to three of his friends: Tim Colvin, Carlos Canton, who died in a motorcycle accident, and Tom Nichols, who drowned at Hermosa Beach Pier in 1988.

Justin Thirsk, Jason's brother and drummer from 98 Mute, appears on the re-recording, both on drums and vocals.