Sam is a Shetland Sheepdog. It is unknown when or how Riggs got Sam. It can be implied, though, he still wanted company after the loss of his wife Victoria and found a dog that can live with him in his trailer.
Sam is shown running towards Riggs' trailer in a beach somewhere, miles away from Los Angeles. He is very loyal to his master, despite his suicidal thoughts and never misses a chance at being with him. Later, when Riggs returns depressed, Sam was witnessing him about to commit suicide in the trailer, but Riggs quickly decided against it. Sam feels uncomfortable whenever he brings some random female into his trailer, especially a prostitute. He is seen one last time near the end of the movie when Riggs spends Christmas with the Murtaughs. He does not get along with their pet cat Burbank.
Sam is seen with Riggs admiring the beach before going inside the trailer to watch The Three Stooges. Sam is later with Leo Getz as he cleans the trailer before his master returns. When Riggs invites Rika Van Den Haas to his trailer, they have sex and he tells Sam to go outside. But when they are ambushed by Arjen Rudd's men in helicopters, Sam barks loudly and alerts them the danger coming by so they are able to escape the trailer on a pickup truck before they ever get killed. Sam makes it to the truck, and he and Riggs drop Rika off at her apartment. After Riggs is knocked out by Vorstedt, he hides in the back of the truck. He's later seen with Riggs as he paces along the beach with Rika in his arms sobbing over her dead body. He's left at home while Riggs and Murtaugh go to take down Rudd and Vordstedt's operation thereafter.
Sam's role is small in this film (he appears in the deleted scene/extended cut of the film) and he is seen with Riggs' new Rottweiler (which he was able to tame) watching The Three Stooges in his trailer.
Sam only appears in one scene of the film, together with the Rottweiler. As usual, Riggs feeds both dogs biscuits in his trailer and then has one for himself.
To view the Sam the Dog gallery, click here.