Mike Dirnt is best known for playing bass in Green Day. He is the band’s bassist and backing vocalist, forming the low end of its classic three-piece lineup with guitarist Billie Joe Armstrong and drummer Tré Cool.
Dirnt, born Michael Ryan Pritchard, co-founded the band with Armstrong in the late 1980s. He originally played guitar, but switched to bass as the group developed into a power trio. That change helped define Green Day’s sound: his melodic, forceful bass parts often move actively beneath Armstrong’s power chords rather than merely doubling the guitar.
His playing is especially prominent on songs such as “Longview,” whose bass line became one of Green Day’s signature musical hooks, and “Welcome to Paradise.” Dirnt has also contributed occasional lead vocals and has played guitar, but those are secondary roles in the band.
Fans may also associate him with distinctive instruments, including Gibson and Fender basses. Those model names describe the equipment, not the instrument category asked about here: the canonical answer is bass.