A good egg
Definition 1 of 1
Pro Tip 1/3Positive Connotation
The phrase usually suggests someone is reliable and pleasant to be around. 
Whenever help is needed, Sarah is there. She's a good egg.
Pro Tip 2/3Colloquial Use
Commonly used in informal settings among friends or family. 
My grandpa can always make me laugh - he's such a good egg.
Pro Tip 3/3Non-Literal
It's an idiom, meaning you shouldn't take 'egg' literally; it describes a person's nature. 
Even after a tough game, the coach praised both teams for being good eggs.