|The title of this article is conjecture based on information revealed in the A Song of Ice and Fire novels or related material and may be subject to change.
Following the Sack of King's Landing and the birth of Daenerys Targaryen, Ser Willem smuggled Viserys and Daenerys across the Narrow Sea to the Free Cities before Stannis Baratheon arrived to seize Dragonstone.
In the books
In the A Song of Ice and Fire novels, Willem Darry was the master-at-arms at the Red Keep and the brother of Ser Jonothor Darry of the Kingsguard. He was a grey bear of a man who was half-blind. He had a gruff, kind voice and big wrinkled hands, soft as old leather.
After the Mad King's death in the Sack of King's Landing and Queen Rhaella's death during labor, the garrison of Dragonstone considered selling Viserys and the infant Daenerys to the new king. However, before they could come to a decision, Ser Willem and four loyal men smuggled Viserys and Daenerys from the island and fled to safety in Braavos. However, Ser Willem was old and some years later he became sick and died, leaving Viserys and Daenerys to fend for themselves.
In "A Feast for Crows" and "A Dance with Dragons," it is revealed Ser Willem and Doran Martell signed a secret pact of alliance between Dorne and House Targaryen in Braavos. The alliance was to be sealed by a marriage between Viserys and Princess Arianne Martell. Ser Willem never told Viserys (nor Daenerys) about the pact. Viserys died unaware, and Daenerys only learns of it many years later when Quentyn Martell arrives at her court in Meereen to propose a marriage between the two of them, given that Viserys is dead.