Charlie Chaplin was influential because he would make himself relatable with his working class audience. He wore clothes with holes in, and his characters, such as the tramp, were rarely upper class.
Buster Keaton was influential because of his slapstick comedy, and his stunts which were physically done through planning and risk. He had a dead pan static facial expression (named the ‘The Great Stone Face’), which made his comedy all the more iconic.
Harold Lloyd was also influential for his physical stunts of comedy, where he put himself in danger, such as swinging from building.