IG series robots... breathing?

grievous was a sentient first, shortly before the clone wars he was a monster general racking up victories in his own planets civil war. His exploits as a commander caught the attention of Palpatine and Dooku who helped organize an accident that left Grievous in pieces but still alive. The Sith gave him a new body and purpose, since the war back home was now over having the jedi intervene and give victory to the other guys, Grievous now had nothing but room to maximize his new role as separatist general full of jedi hate. Not just a droid was the point, and to be honest thinking about Grievous maybe Vader should also have a droid tag, many of his vitals run off machinery