Uthero Zalyne

Uthero Zalyne is an unseen character in Game of Thrones. He was a Sealord of Braavos.

Biography
During Uthero's tenure as Sealord, he revealed the existence of Braavos to the surrounding world, including the Valyrian Freehold. As restitution for the ships stolen from the Valyrians by the slaves who had founded Braavos, Uthero sent envoys from the Iron Bank of Braavos to pay the Valyrians. However, Braavos refused to pay for the slaves themselves. The revelation of Braavos' existence became known as the "Unmasking", and is celebrated annually in Braavos.

Reference

 * "Braavos (Histories & Lore)"