Denys Mallister was played by J.J. Murphy, who died four days after filming his first scene, at the age of 86. Co-creators David Benioff and D.B. Weiss have announced the character will not be recast as Murphy "was a lovely man, and the best Denys Mallister we could have hoped for. And now his watch is ended."
In the A Song of Ice and Fire novels, Ser Denys Mallister is an old man that has commanded the Shadow Tower for thirty-three years. He is the uncle of Lord Jason Mallister. Ser Denys was born at Seagard, a squire at twelve, a knight at eighteen, and a champion at twenty-two years old. He had been a candidate in the two last elections of Lord Commanders of the Night's Watch.
Ser Denys has blue-grey eyes and a long white beard. He has lost almost all his hair and his face is deeply lined though he still has his teeth and is graceful in his movement. In his communication with other people he is very courteous. He is considered cautious and chivalrous. He's also distrustful of ironborn, due to his upbringing at Seagard, which had been built as a defense against raiders from the Iron Islands.