I work with a guy like this. His knowledge base is vast (we're electrical engineers and he's a master of both hardware and software). He's also a shambling zomb

I work with a guy like this. His knowledge base is vast (we're electrical engineers and he's a master of both hardware and software). He's also a shambling zombie from a lifetime of hacking through the night. I'm not exaggerating. He mostly just shuffles through his days, trying to get anything done, but he's just too fried. He rarely sleeps. I've never seen him eat. He won't take vacation days. He seems to have decided a long time ago to just drive himself insane. Honestly, I think if he weren't one of the guys the company can't afford to lose because he knows things about our products no one else in the building does, they'd probably let him go.