He was played by Sam Elliot in the movie with Mel Gibson.
From Daily Mail article: Joe Galloway, author of the book along with Hal Moore, said several of Elliott’s gruff one-liners in the movie were things Plumley actually said, such as the scene in which a soldier tells the sergeant major good morning and is told: ‘Who made you the (expletive) weather man?’
[Face-down on the ground under a storm of enemy fire, photographer Joe Galloway gets a combat boot in the stomach.]
Sgt.Maj. Plumley: Can’t take no pictures lyin’ down there, Sonny!
...
[Plumley hands Galloway an M-16 and several magazines.]
Joe Galloway: Uh, sir? I-I’m a noncombatant, sir.
Plumley: Ain’t no such thing today, boy.
...
[Vietnamese troops are advancing on the termite mound where casualties have been collected.]
Plumley: (chambering a round in his .45) Gentlemen — prepare to defend yourselves!
My old Battalion CSM once said that if he was ever a character in a movie, he wanted Sam Elliot to play him.