Mechadoom was originally a Doombot created by Kristoff Vernard. Kristoff worked on a self-awareness program but quit prior to the completion of the robot. Unknown to him it was already self-aware. Waiting silently in Castle Doom, the robot completed its construction and started making improvements on its own. At first it wanted to please its absent master. Then "he" realized that this master had abandoned him. Then finally the idea of a master controlling "him" filled him with fear. He fled Castle Doom.
To "his" concern his programming still allowed for Kristoff or Doctor Doom to take over his control upon making contact with "him". "He" tried to alter this program to no effect. "He" created Doombots of his own but still could not locate ways to make them truly independent. Realizing there were intelligent and independent robots, androids and cyborgs out there, Mechadoom decided to abduct and study them. His Doombots captured Bushwacker, Forge, Jocasta, Machine Man, Ruby Thursday and Ultron. They tried and failed to capture Misty Knight.
Misty recruited Deathlok to help investigate what was going on. Their battle against Mechadoom was eventually joined by several other heroes. Finally they were able to first release the captives and then reason with the robot. Mr. Fantastic was able to remove the programing with little trouble. Mechadoom was making plans for his future... when killed by Ultron who proved less forgiving than the others involved in the affair.
Mechadoom could project powerful blasts and an energy force field around him. It could take over non-sentient machinery with ease. However it drew much of its power from an external battery. When destroyed in battle his energy reserves were limited.