"Plastic Man" refers to a sample taken from the 1975 spoken word novelty/comic releases:
Unknown Artist - Plastic Man: The Invasion Of The Plastic Men / Metamorpho The Element Man: Fumo, The Fire Giant or
Unknown Artist - Songs And Stories About The Justice League Of America

While "Plastic Man" is not a 'proper' artist, it appears with a 'Featuring' credit on at least this release:
Coldcut - Doctorin' The House (1988)

The sample is also used at least on:
James Brown - The Payback Mix (Keep On Doing What You're Doing But Make It Funky) (1988)
Subsonic Force - The Invasion Of The Plasticmen (1992)
Brainstorm Crew - The Plastic E.P. (1992)
"Something Big" on They Live Long - Born And Healthy EP (1993)
"You Must Learn All Night Long (SWAMP Mix)" on Fantastic Plastic Machine - International Standard: Luxury Remixes US (1999)