Play video content EXCLUSIVE Copyright: Keya Morgan

Stan Lee is mad as hell over reports he's being abused and taken advantage of, because he says they're completely untrue ... and he's going to do whatever it takes to set the record straight.

The legendary Marvel creator tells TMZ ... material recently published about him and his friends -- specifically Keya Morgan -- is nothing but slander. Lee says the claims are "hateful and harmful" and he can't even believe some of the accusations.

Stan's adamant he's not being mistreated, and suggests someone might have a personal vendetta. In any event, he's ready to take legal action against any media outlets wrongly trashing him.