Micah is a butcher's son who has befriended Arya Stark.
He travels the Kingsroad with his father as part of King Robert Baratheon's retinue.
When he is encountered by Joffrey Baratheon practicing sword-fighting with Arya Stark, Joffrey confronts him for 'pretending to be a knight'. Despite his protests that the weapon he was using was only a stick, Joffrey forces him to pick it up. Joffrey sadistically begins pressing his sword against the boy's cheek, which prompts Arya to attack him. Mycah manages to escape but later is killed by the Hound under the orders of the prince much to Ned Stark's horror.
Micah was a playmate of Arya Stark's and traveled with her family to King's Landing. After Arya humiliated Prince Joffrey Baratheon, the prince had Micah killed by Sandor "The Hound" Clegane.