If you hire someone completely unqualified to run a company and he does a horrible job of it, who is ultimately responsible?

And you could fire him at any time but you don't and you just let him keep fucking everything up, who's responsible?

Bonus question, completely hypothetical of course: this unqualified person's contract expires and, on the way out, he sends a violent mob to disrupt the hiring of his replacement, and you still hire him back a few years later, despite him racking up criminal convictions in the interim and showing no signs of improvement, who is responsible for his continued fuckups?