He was voiced by John Stocker.
The Second Show Ever
Sam & Max escort an elementary school class in their DeSoto that manages to reach the vastness of outer space. There, they cross paths with Lactose the Intolerant who proclaims himself to be the "Custodian of the cosmos, Caretaker of the constellations, Sweeper of the corridors of time". As part of his duties, he seeks to destroy the Earth due to it being an "impunity". Through a psychic connection with Max, Sam attempts to persuade Lactose otherwise by showing the various inventions of humanity. However, this only further encourages Lactose to see through his mission. He also endangers the class in the DeSoto, although he shows a fondness for the car itself.
The duo then challenge Lactose to a thumb-wrestling match as a way to prevent Lactose from destroying the Earth. Max then headbutts the giant alien and the two are seemingly killed. But then it is revealed that Lactose has only found work as the school's lunch heater. He plots his revenge against Sam and Max.
The Final Episode
Amidst Mack Salmon's collective of villains, Lactose stands guard outside the door of the plane carrying them to keep Sam and Max from escaping. Sam and Max defeat him by severing the chord connecting him to the plane which causes Lactose to plummet to the ground below.