Denys Mallister is a knight and the commander of the Shadow Tower, one of the three still operational castles of the Night's Watch. He is the uncle of Lord Jason Mallister of Seagard.
In the books
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, was 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.