
Acting
Michael Edward Mills (born December 17, 1958) is an American multi-instrumentalist, singer, and composer who was a founding member of the alternative rock band R.E.M. Though known primarily as the bass guitarist and backing vocalist of R.E.M., his musical repertoire also includes keyboards and occasional lead vocals. He contributed to a majority of the band's musical compositions and is the only member to have had formal musical training.
Description above from the Wikipedia article Mike Mills, licensed under CC-BY-SA, full list of contributors on Wikipedia.

BP Fallon: Rock'n'Roll Wizard
as Self

Weirdo: The Story of Five Eight
as Self

Finster

Chuck Leavell: The Tree Man
as Self

R.E.M. - Monster
as Himself

R.E.M. - Automatic for the People
as Bass guitar, backing vocals, organ, piano, accordion, double bass

R.E.M. - Automatic Unearthed

R.E.M. - Out Of Time
as Bass

R.E.M. Unplugged: The Complete 1991 and 2001 Sessions

Paradise Garden: Howard Finster's Legacy
as Self

Seven Ages of Rock
as Self · 7 ep.

The Colbert Report
as Self · 1 ep.

Boston Public
as Self · 1 ep.

Parkinson
as Self · 1 ep.

The Simpsons
as Mike Mills (voice) · 1 ep.

MTV Unplugged
as Self · 2 ep.

MTV Video Music Awards
as Self · 2 ep.

Austin City Limits
as Self · 1 ep.

Rockpalast
as Self (bass vocal) · 1 ep.