Human(we think), male, 62 years:
He is a gaunt and thin man of moderate height. While quite thin, he has ripcord muscles providing him great strength and speed. He is quite pale, with sunken cheeks and eyes. (He does avoid the sun, so he has a parasol when forced to go outside). His eyes are vibrant blue which sets off his nearly white skin. He has pattern baldness, empty on top, long white hair along the sides and in back. His smile seems carniverous.
His clothes are expensive, but dated. They are dark and velvet, they scream GOTH. However, we are a few centuries before that. He favor’s dark colors because of his pale coloration.
He is a minor noble with nothing of lands or money. He came to his current senechal (or factor, or guy in charge) position quite by accident. He was down on his luck at the right time at this place. He utilizes his keen intellect, commanding presence, and understanding about “how things work”, to keep the operation running.
Note: He is quite skilled at military arms, though it has been a decade or so since he actively practiced it. He is pretty dangerous for a man his age.
Depending on the level of magic in the world, he might have an item or two squirlled away.
He does have The Keys to everything. He might also have some domestic magic items in his charge.
He will have a minor magic weapon that fell into his possession two decades back. He is keeping it for a special occasion, like the castle being overrun.
He is the “gatekeeper” for many things in the castle. He can arrange appointments, or make sure you are never seen at court. He can make sure you are comfortable and get a good room or feel ill welcomed and have a lumpy place to sleep. A simple comment and no servant will be anywhere near you. He has an inhuman amount of pull in the kingdom even, as decades of favors have been accumulated.
He is normally quiet, very quiet. He walks quietly. He writes quietly. For decades he was a aide, always there never seen. These habits are still with him, even though he is in charge.
He is constantly sneaking up on people and suprising them, especially if they are doing something they shouldn’t.
He is aware that his presence unnerves people. He will not do anything to diminish people’s discomfort around him. In fact, he seems to work on his “scary” image. He will utilize this unnerving to get people to do what he wants.
“Please young lady, I will not bite you. Now go and ......”
He is unfailingly polite. His threats are more by tone of voice and veiled references, than simple barbaric descriptions.
“Once you get used to him, he is quite a nice man.” ... “However, he is hard to get to know.”