From Muppet Wiki

Old Major is an aging prized show pig in Animal Farm. Nearing the end of his life, Old Major wishes to impart wisdom to his fellow animals, encouraging them to rejoice in the nobility of their "animalism," care for each other collectively, and fight to eventually be freed from men. During the meeting at the barn, the loft gives way, and the fat hog falls to his death. His memory is honored by the animals, but later abused by Napoleon, who goes so far as to bring the rotting head of the boar, saved from the Jones' icebox.

In the original George Orwell novel, Old Major was largely inspired by Karl Marx.