"Himself": it's clearly a blend word of "him" and "self". But in what situation would those two words in that order make any sense at all? None that I can think of. He killed himself => He killed him self. Convention ensures that we know what that means but, grammatically, it is a ridiculous sentence. He killed him? Sure. He wrecked him truck? He found him keys? No, and no.

Now consider "Herself", "Yourself", "Myself". Those make perfect sense; it's her self and your self and my self. The self in question belongs to her or you or me. She can laugh at her self. You can see your self in the mirror. I burned my self. Yes. All fine. He touched him self. No! Wrong!

The object form of "he" - "him" - doesn't show possession of the "self". "Her", "Your", "My", "Its" - all possessive. "Him" - objective.

What we mean to say, but are discouraged from saying is "his-self". He threw hisself off the cliff. Yes! It was his self that he threw off the cliff. But "hisself" is non-standard and should only be spoken by ignorant people who don't know that the non-grammatical "himself" is the correct. Follow the rules, except for the ungrammatical exceptions.

Also wrong: themselves (theirselves).