a best friend
A best friend is the person who will punch your face for you when you’re getting bullied and also cover for you when you’re being a total idiot.
You: 'He called me a nerd.' Best friend: 'I’ll call him a loser.'
You: 'I told the teacher I was sick.' Best friend: 'I told the principal I was sick too.'
You: 'I stole his lunch.' Best friend: 'I stole his pants.'