He is a member of the Sons of the Harpy.
Daario Naharis and Grey Worm find him hiding in a house in Meereen and arrest him. Daenerys Targaryen consults her advisors and Mossador urges her to kill him to send a message to the Sons of the Harpy. Ser Barristan Selmy advises her to exercise caution and give him a fair trial as a way of maintaining the equality among the citizens, to which she agrees. Before the trial can take place, Mossador enters the Son's cell and murders him. Mossador dumps his corpse in public, his face covered by his harpy mask and writes "kill the masters" on a wall in his blood. He is executed as punishment for this.
|Season Five appearances|
|The Wars to Come||The House of Black and White||High Sparrow||Sons of the Harpy||Kill the Boy|
|Unbowed, Unbent, Unbroken||The Gift||Hardhome||The Dance of Dragons||Mother’s Mercy|
In the books
In the A Song of Ice and Fire novels, there is no parallel to this character. The Brazen Beasts (an army of watchmen formed by Daenerys) have taken dozens of the Harpy’s Sons, and those who have survived their capture have yielded names when questioned sharply, but the identity of their leader remains unknown.