The Apollo 13 actor said cancer eventually paralyzed ... and he accomplished great things in those final months," Gary Sinise added in his tribute. "Thank you, Mac. You did it.

Actor Gary Sinise -- a tireless advocate for U.S. veterans -- announced Tuesday his son McCanna "Mac" Sinise has died of cancer at the age of 33.

At the age of 18, Gary Sinise co-founded the Steppenwolf Theatre ... He has also starred in Apollo 13, Ransom, and many more films. He has received Tony Award nominations for acting and directing.

Fact-based drama about the ill-fated 1970 Apollo 13 mission to the moon ... With Tom Hanks, Kevin Bacon, Bill Paxton, Ed Harris, Gary Sinise, Ed Harris, Kathleen Quinlan, Mary Kate Schellhardt ...