Richard Riehle -- famous for his role as Tom Smykowski in "Office Space" -- is dead ... TMZ has learned.

Friends of Richard tell TMZ ... he died of natural causes last Thursday in Los Angeles.

He was an acclaimed character actor, appearing in over 400 projects during a long career in Hollywood.

Richard's best known for his work in "Office Space" ... he plays Tom, the product manager who gets laid off from Initech, survives a hit-and-run accident, and lands a massive financial settlement that allows him to follow his dreams and build his prototype "Jump to Conclusions" mat. He's got tons of memorable scenes and lines, and is a cult favorite.

The last time we caught up with Richard was back in 2018 in Los Angeles, after he had just gotten back from filming the Lifetime holiday movie "A Very Nutty Christmas" with Melissa Joan Hart.

Richard was 78.

RIP