Amber Heard ''calls the shots'' in her relationship with Johnny Depp.

The 27-year-old actress is believed to have just got engaged to her 'The Rum Diary' co-star and friends say she's the woman who has finally tamed him.

A source who knows them both said: ''Amber has called the shots since day one, dictating when they went public, for example. She's half his age and that's part of why he'll do whatever she wants in order to keep her.''

Another source added: ''He has definitely toned down his behaviour since he started dating Amber. He acts like a mature and charming man now.''

The 50-year-old actor - who has daughter Lily-Rose, 14, and son Jack, 11, with former partner Vanessa Paradis - is said to be attracted to the way Amber has her own way of doing things and doesn't ''go with the flow''.

A musician friend of Johnny's said: ''Amber is a female version of Johnny. She's sort of kooky and outspoken, and while that would intimidate many guys, it is a turn on for Johnny.''

Another friend told People magazine: ''Amber has a mind of her own and doesn't go with the flow. This chick challenges him on so many levels, and that has changed his attitude on settling down.''