The PS2 had two CPUs inside, one of which had GPU-like features. To differentiate them, one was called the IOP = Input Output Processor and the other the EE = Emotion Engine.

It was a surprisingly powerful system at the time and it took developers years to understand it well enough to take full advantage of the hardware. But the ability to have 2 CPUs run simultaneously and interact with each other allowed for A LOT of crazy optimizations that I haven't seen since.