In old Greek myths (and most other civilisation's myths too), if a God makes a promise they absolutely must keep their end of the bargain and cannot go back on their word no matter how evil they are. Since Unicron is a God is he also bound to this? In other words has Unicron ever actually told a blatant lie in any Transformers continuity?

i dont think hes ever out right lied. hes always been quite up front about his distroying ways and he kept his part of the deal when giving megs his new body

Unless Unicron vowed his oath on the River Styx then he can do whatever he damn well wants.

I don`t think Unicron was ever even called a god. I think he`s more like the transformers ultimate demon.

I see Unicron not as a god but a the devil so he can lie if he wanted to. Just like Q the god of lies.

assuming he is a god, if lieing is in question its prolly just the "read the fine print before signing" sorta thing. like him psychicly hurting galvatron when he failed to destroy ultra magnus in tftm, thats a case were megs didnt read the fine print when he sold his spark to unicron. "may be subject to psychic attacks if unsatisfied with progress of subject... unicron wtf?"

[unicron] SIGN! [/unicron]

I believe in the comic book or atleast in the japanese continum he was refered to as a dark god.

And that's an interesting thought there. He never really lies in the movie, he just hides facts. Like "yeah I'm giving you a body, but I'm also fallowing you to your planet so I can eat it for brunch"

Unicron from G1 TV show was not a god.  He was some alien/guys creation that went on his own.  This is noted in season 3.

i think weve has this discussion before about the "god" issue. i dont think we should go into this any further.

I don't remember a time were he ever went back on his word, the closest in any continuity is US Marvel Unicron sends Hook, Line, and Sinker to get a Galvatron from another dimension. Galvatron complains that he already did his duty and Unicron promised him Earth, they reply, "Different Unicron."