Sir Rupert Gale was affiliated with Penelope Fittes. His father had helped Marissa Fittes; and, now, Rupert Gale served Penelope. His role was to teach agents in sword fighting and martial arts.
He was a young man (but adult, age not given) with blue eyes, blond hair, and a mustache. He wore a strong sent of aftershave.
He carried a sword-stick (a.k.a cane-sword = sword hidden within a cane/walking-stick) as his primary weapon.
He first appeared at Book 2 as an unnamed "collector" at Julius Winkman's auction for the Bone Glass. He had much interest on buying the artifact but Anthony Lockwood and Lucy Carlyle, wearing masks, had stolen it.
He appeared next in Book 3 as a companion of Penelope Fittes meeting Lockwood's team, officially, in the carnival. There, he immediately hinted that he recognized the chins of the pair - Lockwood and Carlyle - who attacked the auction of Winkman. Soon at the parade, the carnival attack happened when two conspirators threw ghost bombs at the gathering crowd. Sir Rupert Gale, after Lockwood and Carlyle, gave a chase to the remaining assailant (the other one was killed by Steve Rotwell by now). The assailant was able to escape and left the pursuing trio alone. Gale initiated a combat against Lockwood that was quickly halted when other people have appeared behind them.
He was seen next with Penelope Fittes when the pair visited Lockwood & Co. at 35 Portland Row (Book 4). There the two asked the small agency to join Fittes Agency. But when the youths declined, the pair gave their threats and warnings for the youths to stop investigating the gates to the other side. From this point on, Rupert Gale was clearly a fixer, the one who does the dirty work, of Penelope Fittes.
He threatened Holly Munro while the girl was out for groceries (Book 5). He arranged the murder of Adam Bunchurch, head of a small agency. Also he ordered some men to rough up George Cubbins (confirmed by Lucy in Book 5:23).
Later, Rupert Gale asked Julius Winkman to prepare an attack at the home/base of operations of Lockwood. He joined in the siege of the house. The youths escaped by hiding in the Other Side. Rupert Gale was the only one to recognize the cause of disappearance of the youths and so he destroyed the "gate" (to the other side) that the youths used.
Within the Fittes House in the Hall of Pillars, Rupert Gale confronted again Lockwood & Co.. The youths shot blasts that shattered the Relic Columns (where infamous ghosts were kept). One of the ghosts called the Gory Girl snatched and killed Rupert Gale.