Brian (Saturday Supercade)
From the Super Mario Wiki, the Mario encyclopedia
Brian first appears at the beginning of the episode, where he was escorted to a local pet store while Solmes and Kenworth discussed their plans to steal the mansion's jewels. When he saw Donkey Kong, he "purchased" him and took him back to the limousine to the mansion.
Brian then had his birthday party with Donkey Kong, riding along with him on his new bike. They crashed into Kenworth while he was trying to open the safe. When Brian asked Kenworth why the safe was open, Kenworth "claimed" that a "burglar" was trying to steal the jewels. Brian and Donkey Kong began preparations for the thief's "return".
Snooping around, Brian and Donkey Kong caught Kenworth attempting to call a local zoo, telling them that Donkey Kong was an "escaped animal". Brian fired him without question and ordered Donkey Kong to literally boot him out.
When Mario and Pauline arrived at the scene and attempted to enact their plan to capture Donkey Kong, Brian incorrectly deduced them as the zoo employees, and immediately cut Donkey Kong free without being spotted, allowing him to sabotage Mario. Later, as Brian took Donkey Kong to a nearby golf course, he witnessed Mario's face-off with Donkey Kong before both of them ended up in a concrete booby trap set up by Solmes and Kenworth. As the villainous duo stole the safe, Brian began to realize that Mario and Pauline were not truly hostile.
As Brian was searching through the mansion corridors for Solmes and Kenworth, he and Donkey Kong spotted them and immediately recognized them in their ape costumes they had changed into almost immediately before, and knocked them both out with bowling balls and into the same zookeeper Kenworth had called earlier. Later, Brian was seen talking about the climactic events to a girl, but gave some credit to Donkey Kong for helping him.