[Gladiator, sort of...] Was Commodus the only one to do the thumb-thing?

Okay, sorry for the odd question. I know if I google "ceasar thumb down" etc, I get results of Commodus from Gladiator. Which I can understand, but was Commodus (in general, not the movie), the source of this? Or did he just continue it when he reigned?

I always thought it was from Caesar, as in, I remember (this is gonna age me, lmao) an old Foamy the squirrel rant where he says something along the lines of "this guy sticks his thumb in the air like he's fucking Caesar" so I always thought Caesar was the one who was the original gladiator-watching thumb up/down.

But my knowledge on this was never very steady. Is it thought that Caesar did this before Commodus, or is Commodus the original of it?