The old thieves at the museum (Real names unknown) are two elderly burglars who are pretending to be innocent old people who are visiting the museum in Bay Area.
They want to steal a old and giant nugget of gold that is being displayed in the museum and their plan was to hide in the museum and wait till it was closed. Earlier Gus dysregulated the security system when he wanted to grab the gold, so the thieves have it easy.
Because of Gus his stupidity he, Tommy and Lola were kicked-out of the museum. Tommy loses Robotboy who stays behind in the museum, so they decide to return. There they catch the thieves in the act of stealing.
The two aren't happy with that and they decide to get rid of the snoopers. First the kids laugh at them but it is revealed that their walkers can be rebuild into fast flying machines.
First they can't catch Tommy, Lola and Gus. The big men in the blue and Tommy are fighting by using swordfishes. The little men in the yellow shirt want to attack Lola and Gus, but she can hold him off by grabbing a ugly octopus (who looks like Gus) who squirts oil in the old men's face. But when Tommy is defeated, the old thieves catch the kids with a net. Just before the old men in the yellow shirt stabs them with the swordfish, they are being eaten by a dinosaur who is controlled by Robotboy who finally noted that his friends where in danger.
The museum director comes in with two security agents and notice the mess and the thieves. The thieves give themselves over and return the nugget of gold to the director. Then they are being arrest and discharged.
They are both very old and fragile. But they seem to be in good shape and still able to make plans. They live together in the same retirement home.
It seems like the big old men with the mustache and goatee is the leader and the little men with white hair is the fighter of the two. The little man also wears a toupee.
They both appear in the season 4 episode Bowling for dummies, but in two different bowlingteams. The little man doesn't wear his toupee in this episode.