Name: Alec McMahon MacKenzie
Position: Master of Horse of Castle Leoch
In the books, Old Alec was blind in one eye and wore a patch over that eye. He was in charge of the MacKenzie stables, and Jamie was working under his supervision.
He first appeared in the S01-E02 Episode Castle Leoch when Claire tool lunch to Jamie at the stables, and Old Alec told him to get back to work.
He was mentioned in the S01-E03 Episode The Way Out, when Jamie and Claire were talking and he told her that he didn't have her remove his bandages at the stables because he didn't want Old Alec to see his scars. He explained that Alec knew he'd been flogged, but knowing and seeing are two different things, and he didn't want Alec to pity him.
Then in the S01-E04 Episode The Gathering, Claire went to the stables to procure a horse for the boar hunt the next day. Alec introduced her to a filly named "Brimstone" which had her a bit worried, until Alec told her that Brimstone was a really good, gentle horse, but she wwould turn for home at the first opportunity. He also informed Claire that it would be for the best for all concerned if Jamie kept to himself until the gathering was over.