Autobot Spike

Sparkplug constructs a new robot which is given the moniker Autobot X. However, during testing the robot is proven to be unstable, Sparkplug cannot control it and it is shutdown and put into storage. Soon after Spike is injured in a conflict with the Decepticons. In order to save him his mind must be transferred to Autobot X so that doctors may operate on his fragile body. Autobot X's unstable mind fuses with Spike's, who is in turn influenced by Megatron to betray the Autobots. Only the near death of Sparkplug prevents Spike from continuing his rampage, shaking him from his madness. Finally, following his surgical procedure, Spike's mind is returned to his own body.

From Teletraan I: The Transformers Wiki, a Wikia wiki.