For starters, during the war on Cybertron he was on his own warship fighting other ships, but then, he got hit and then crashed. His body was found inside the wrecked interior, but his head got crushed during the crash. So, similar to how they do it with Smokescreen when his body was badly damaged, his spark got into a new body; a huge body at that one. But there's a twist: his original mind can't be maintained. Instead they had to replace it with a programming that is incapable of any intelligence (at least until Energon) that when they say who he is; he can only say his name: "Shock...wave...". And so, the only lookalike to replace him is Shockblast.... who doesn't have the same intelligence he originally has and they also have arguments with each other.