The Microwave is one of the major characters from The Brave Little Toaster Goes to Mars.
The Microwave is first seen in the kitchen where he boasts to Ratso and the appliances about how useful he is and how useless they are, before he helps heat formula for the Master's baby, Robbie (the Little Master). He then proves it when the Master himself places a bottle of formula inside the Microwave and warms it up for the Little Master. Ratso and the appliances dislike the Microwave due to his boastful nature and how he offends the other appliances by stating that the Master will never use them again.
Later, when the Little Master is abducted, Toaster and the other appliances use the Microwave on a rescue mission to travel to Mars and take some cheddar cheese flavored popcorn, which they place inside of him, to help them fly. He pops the unwrapped bag of popcorn, which is organic and provides the fuel the appliances will need to help them navigate through space. After the Little Master is found and rescued, the appliances prepare to travel home. When they run out of the cheddar cheese flavored popcorn, Tinselina, an ACAM that the appliances befriended on Mars and who chose to go back with them, helps out by giving up her clothes and hair and placing them in the Microwave so that they have something organic to get back to Earth.
The Microwave is last seen playing tic-tac-toe on his touch pad with Ratso and beats him, much to Ratso's discouragement.