Edmund is the illegitimate son of the Earl of Gloucester and brother of Gloucester's legitimate son Edgar, who stands to inherit his father's title and lands while Edmund gets nothing. Edmund is a cunning and successful villain. He manages to make their father believe that Edgar is plotting against his life, forcing Edgar to go into hiding.
Then Edmund becomes Earl of Gloucester by betraying his own father, who is trying to help King Lear regain his throne by giving aid to the invadiing French army led by Cordelia. Edmund seems on his way to becoming a king because his good looks combined with his vicious character have made both the widowed Regan and her sister Goneril fall madly in love with him. Goneril is plotting with Edmund to murder her husband the Duke of Albany, but they are exposed by Edgar, who subsequently kills Edmund in a duel.
It is generally believed that Edmund's villainous character is attributable to divine punishment for Gloucester's fornication as well as to Edmund's bitter resentment of society's prejudice and discrimination against bastards. Edmund reveals everything about his character, his motivations, and his plans in a soliloquy at the opening of Act 1, Scene 2, beginning with:
Thou, nature, art my goddess; to thy law
My services are bound.
He is one of Shakespeare's cleverest and most unscrupulous villains, along with Iago and Richard III.