Yes, he's SO big, he doesn't even fit on a 17" monitor!
Actually, he's about 50 times bigger than Willie Trombone, and yet they're kind of brothers. Bil was made by Ottoborg as one of three Big Robots, the builder, to help with the houses of Otto's sons. But you can read all that in the Chronicles (in the Hall of Records) while you're there.
Important for the story is that Bil and Willie were best buds for a loooong time, until Klogg took over the Neverhood and turned Bil to 'bad'.
The bloo teddy you see next to Bil here was a present by Hoborg, and the robot loves that thing a LOT.