Bitzer is one of the main protagonists (sometimes antagonist) in Shaun the Sheep and the deuteragonist in the movie.
He is voiced by John Sparkes, who also voiced his owner, The Farmer.
the brown, long-suffering sheepdog, only wants a quiet life - but this is the last thing he is going to get when Shaun The Sheep is around. He is obviously on the same side as Shaun and the flock, but even though he is also very loyal to The Farmer, he will never let him know about the animals' intelligence. He somewhat bears a resemblence to Gromit. On "Off the Baa!", he acted referee for the football game, so he probably knows a little football. Bitzer also lets Shaun have the chart and whistle and be in charge if the farmer is sick or something.
Shaun the Sheep Movie
Shaun is reunited with Bitzer in the animal lock-up, and with the help of a homeless dog named Slip they manage to escape while imprisoning Trumper. They find the farmer, but he does not recognize Bitzer and Shaun, who is heartbroken.
Feeling unwanted, Shaun, Bitzer, and the flock make a makeshift home in an alley. Their spirits are revived when they stumble upon evidence of the farmer's memory loss. They devise a plan which involves putting the farmer to sleep again, returning him to the trailer on a pantomime horse (really the flock of sheep in an elaborate disguise), and hooking the trailer up to a bus returning to Mossy Bottom. The plan is initially successful, but they are pursued by Trumper (having escaped the lock-up), who is now intent on killing them outright.
At the farm, the group hides in a shed. Trumper, using a tractor, tries to push the shed into a nearby rock quarry.
The farmer and the animals have a renewed appreciation for each other, and the next day the farmer cancels the day's routine activities for an official day off.