In a film or a story The Lead Sled Dog is the character who sets the pace for everybody else. He gives the film a metronome beat. He's like the base player in a jazz combo. Other actors find themselves naturally calibrating their performance to the rhythms of the Lead Sled Dog. They wrap around it. They bounce off it. If your script or your actors don't have a Lead Sled Dog then you have a rudderless ship and you're screwed.
Sometimes the Lead Sled Dog is the star. Sometimes not.
An example of the Lead Sled Dog as star is Jackie Gleason in the old Honeymooners TV series. Look it up on YouTube. Even when Gleason wasn't physically in a scene his presence was felt. Other actors made their characters a counterpoint to what Gleason was, so that when you finally see him his over-the-top character seems even more outrageous.
An example of The lead Sled Dog as supporting actor is Danny Glover in the film, "Lethal Weapon." [Glover is obviously a first-rank star in this film, and is fully the equal of Gibson, but I'll treat him as a supporting actor just to make my point more clearly.]
Granted, Gibson is the box office draw, the protagonist, the handsome, driven guy who makes things happen. But the Lead Sled Dog? Nope.
The lead dog in that film is Danny Glover. He's the reactor who's constantly amazed by Gibson's character, who defines Gibson for the audience. Without Glover the Gibson character is just a suicidal crazy guy. With Glover, Gibson is evolving and heroic, someone who's worth taking the trouble to get to know.
Another example: Laurel and Hardy. Who's the Lead Sled Dog there? It's Hardy. Laurel does stupid things that make Hardy react and Hardy is one of cinema's great reactors.
Who's the Lead Sled Dog in Ren and Stimpy? Answer: Stimpy. Stimpy establishes the beat that underlies the story. [Note: John says the lead sled dog in that series was Mr. Horse.]
Who's the lead dog in the Andy of Mayberry show? Andy Griffith! You watch the show for Don Knotts but Knotts organizes his performance around the pace layed down by Griffith.
Interesting, eh?
