Possible Clues:

• His feast day is December 26
• it takes a saint to encourage a fowl to walk
• Boxing Day saint
• 'It' was one of his favourites, written up for sort of party piece
• With 8-Across, comic named one of Time's '100 most influential people' in 2006
• Author King
• Boxing day is St -'s day
• English king from eleven hundred and thirty five
• Does the saint encourage the fowl to use her feet?
• - Sondheim, composer