Who is Mr. Grin from Stormbreaker and what is their importance?

Mr. Grin is Sayle's butler. Mr. Grin had once been a carnival performer who worked with knives. One day Mr. Grin is distracted as he attempts to catch a knife in his mouth. The knife cuts him from ear to ear, leaving him with a scar that looks like a deranged grin. Mr. Grin works for Sayle and he coordinates the criminal activity as well as being the one who deals with people who appear to present an obstacle. Mr. Grin is the one who stops Alex from escaping the house and is the pilot who flies the cargo plane that delivers Alex to London. Mr. Grin dies when Alex detonates a smoke bomb in the plane while Mr. Grin is still flying.