In the story was jotun daughter of Ymir, one of the first being, her brother was Mimir. Her hair was white as snow and she used to paint her face and breasts with blood of her prey or victims XD She was known for her wild personality and crazy behavior. She was feared by both Jotnar and Asgardians ( and other realms XD ).
Still she was beautiful and very desired. The (un)lucky man who tamed her was Bor, king of Asgard and forced her to wed him.
But Bestla was too wild and too headstrong to conform to the life of Asgardian women and Asgardian life itself. She wore her blue skin and threw tantrums when she can :D
She bore Bor his only son Odin (so she is grandmother of Thor…so we know now after who he has his wild temper )
Besla died shortly after the birth, even she was stong woman, no Jotun can stand Asgardian weather and birth of on in his/her natural form.
In the end Bor swore, that no Jotun will ever sit on Asgard throne again.