Who is the traitor that Duncan executed in Macbeth? Who was Thane of Glamis and Thane of Cawdor before Macbeth?

Macbeth is the Thane of Glamis at the start of the play.  We have no idea who held this title before he did.

The Thane of Cawdor was leading another group of troops against King Duncan.  When Duncan is told of this, he has the Thane of Cawdor executed.  There were three leaders who were fighting against Duncan.  Cawdor was one of them, Macdonald was another.

So the traitor that the king executes is the previous Thane of Cawdor.  After he is executed, his title is given to Macbeth as a reward for how well he did in battle.