“If Pharaoh demands that you work a sign or wonder, you shall say to Aaron: Take your staff and throw it down before Pharaoh, and it will be changed into a snake[Heb לְתַנִּֽין (Tannin), Gk δράκων (drakon)] .”–Exodus 7:9
HOWEVER, this like most translations says “snake,” but this is NOT the ordinary word for snake. Tannin can also theoretically refer to a **crocodile **or **cobra **according to one Hebrew scholar, in addition to a mythical “dragon.”
In Gen 1:21 one translation I read translated the word as “titans” haha.
In Job 7:12 tannin is usually translated as “monster” or “whale” , or even dragon. (Imagine if Aarons staff actually was turned into a whale!)
In other verses the word I’ve seen has been also translated “jackal” or “ostrich”.
In anycase the word tends to suggest a scary, or threatening animal that is generally not liked.
I suppose that is why dragon is used in Rev 12,13,16,20