Some Prof. Gerald Robotnik Headcanons
Gerald loves his grandson dearly and is more likely to believe what Ivo/Julian tells him. Despite this, he's not a fool, but rather lets emotion blind his better judgement... a mistake he has made countless times in the past.
Overall, the professor is very friendly, unless given a reason not to be. It takes a lot to get him truly angry, but he does have a few key buttons others should likely not push.
Anything to do with G.U.N. displeases him. Don't talk about it, don't mention it, don't go near it-- he hates them.
While he'll usually leave most people alone, if given the chance, Gerald will re-program machines in his favor, or prank/screw with his enemies in any way he can.
The professor is rather good at mind games, and knows how to tell a lie.
One has to remember that this is a relative of Julian Kintobor / Ivo Robotnik-- he's no pushover. Many of the classic Kintobor traits are present in him, the one he seems to lack is the "truly evil" (as many consider it) trait. In reality, he doesn't lack this at all-- his attempts to destroy the planet in revenge alone prove that, but there's much more evidence than just that.
Visionary or madman? The line between them does not exist within Gerald.
Maria is a sore subject, though he doesn't mind talking about her a little. Ivo / Julian is also a sore subject, for different reasons.
Those who work for G.U.N. immediately become enemies to Gerald.