Reflexes with 自分

In English, you don't say "Jim broke Jim's watch" when there's just one Jim. You say "Jim broke his watch", or sometimes "Jim broke his own watch". You don't say "Jim hurt Jim", or "Jim hurt him", you say "Jim hurt himself".

"His own" and "himself" have the property of being "reflexive". When you need to do something reflexive in Japanese, 自分 fulfills this behavior.

自分の体を食べた
It ate its own body

自分で遊ぶ
Plays by himself

自分 can sometimes be used by some speakers as pronoun, usually first person (like 私, etc) but sometimes also as second person (お前, etc). This is a specific usage that does not mean “one’s own”. It’s just a normal pronoun. Context and experience will tell you how it’s being used.

Sometimes 自分 can be emphasized with 自身:

そこにいたのは、自分自身だった。
The one who stood there was he himself.