"Doofenshmirtz can be so stupid!
Dr. Destrucción is one of Doofenshmirtz's friends and helps with his plan in "Check-Mate Inator". He is obviously smarter than Doofenshmirtz because he knew Carl the Incognito would mess up. He knows and knew about the O.W.C.A., but they did not know about him. Destrucción translates to destruction in Spanish. He has absolutely nothing to do with Dr. Destructicon from "One Good Scare Ought to Do It".
He wears the general clothes of pants and a t-shirt like a normal person. He also wears a long cape and a eye mask to cover his , well, eyes.
He also wears a fez.
Strange clothes for an evil scientist.
He seems to be a good friend of Doofenshmirtz and help him in his plans sometimes. He also talks with Doofenshmirtz alot, possibly over tea or coffee. However, he really thinks Doofenshmirtz is an idiot.
Phineas Flynn, Ferb Fletcher and Their Friends
He doesn't seem to like them that much as he nearly assaulted, and possibly destroyed, them after helping with the Check-Mate Inators. He especially doesn't like Phineas, because he seemed to stand up to him.
Candace was in the same situation as Phineas and Ferb, but he probably thinks she's annoying because she told him to calm down.
Perry the Platypus
Perry the Platypus was about to be defeated by him when Perry cheated and attacked Doofenshmirtz. This probably made him very angry because he thought people were decent, and would play by the rules. Perry obviously showed him them some people are sore losers, and will do anything to win, or defeat evil, for that matter.