Desmond

Desmond was Grand Maester during the reign of Maegor the Cruel. He was the last of three Grand Maesters executed by Maegor.

Biography
Desmond was beheaded by King Maegor for treason, having disagreed with the king.

In the books
In The World of Ice & Fire and Fire & Blood, Desmond assisted in the delivery of the deformed stillborn child of King Maegor and Queen Alys. Maegor blamed everyone who had assisted in the delivery, and ordered several executions, Desmond included.