Stanley

Stanley is a bug exterminator and Mario's cousin as well as the protagonist of the game Donkey Kong 3. In this game, Stanley uses his Bug-Spray Gun to do battle with Donkey Kong and several insects in a greenhouse. Presumably, Stanley managed to defeat Donkey Kong and sent him back to where he came from.

Donkey Kong 3
This time not only had insects infested his greenhouse but also Donkey Kong was trying to cause damage. Donkey Kong would pester bees in their hives to attack Stanley. Stanley would spray Donkey Kong with his Bug-Spray Gun (who was hanging from two vines) and he would be pushed upward by it and eventually end up with his head stuck in a beehive at the top of all the vines.

The Saturday Supercade
Stanley made one appearance in the television series Saturday Supercade, in the Donkey Kong episode "Greenhouse Gorilla", where he's the owner of a greenhouse. Here he's seen taking care of a carnivorous plant called Herman, but then a thief (only referred once as Mr. X) steals it while Stanley is occupied bugspraying a bug. The thief then convinces Donkey Kong that Stanley is the one who wanted to hurt the plant, so he starts throwing beehives at him. Once again Stanley is too occupied fighting the bugs and lets the thief and Donkey Kong run away with Herman. Stanley then join forces with Mario and Pauline and starts chasing them. After a confrontation at a supermarket, and one at a manor where a 'grand ball' was taking place, Pauline convinces Donkey Kong that the thief is the evil one, so they finally defeat him with the ape's help. The thief is finally arrested and Herman returns to Stanley, but Donkey Kong runs away once again. 

Donkey Kong 3 (Game & Watch)
Stanley's greenhouse was again attacked by Donkey Kong, who this time had a Bug-Spray Gun, which in this game shot water bubbles instead of bug spray, of his own. Donkey Kong and Stanley stood at opposite ends of the greenhouse and sprayed the bug spray at bees to move them toward one another. After sending the bees to Donkey Kong and them stinging him enough times, Donkey Kong eventually left again.

Game & Watch Gallery 4
Stanley appears in this game as a playable character in a port of Donkey Kong 3 (Game & Watch) which is one of the many Game & Watch games ported into this game. A modernized version is featured, however it is set in a Ghost House rather than Stanley's greenhouse, Mario replaces Stanley and Boos and Fireballs replace the Bees.

Super Smash Bros. series
Stanley appears in Super Smash Bros. Melee as one of the many collectable trophies. Mr. Game & Watch uses Stanley's Bug-Spray Gun as a weapon called Greenhouse.

WarioWare: Twisted!
Stanley appears as a playable character in one of 9-Volt's Microgames. In this he must do as he did in Donkey Kong 3 and spray Donkey Kong until he goes up and gets his head stuck in a bee hive.

WarioWare: Touched!
Stanley appears in 9-Volt's Microgame Donkey Kong 3. In this microgame, the player must blow at the microphone to make Donkey Kong move to the top, and Stanley, instead of spraying Donkey Kong with his Bug Sprayer, he blew clouds out of his mouth to make him move into a bee hive.

WarioWare: D.I.Y. Showcase
Stanley appears in one of 18-Volt's Microgames. In this game he must do as he did in Donkey Kong 3 and spray him until he goes up and gets his head stuck in a bee hive.

Trivia

 * The Game & Watch game Greenhouse has a premise and gameplay very similar to Donkey Kong 3, often leading to the belief that they both star the same character, but this was never confirmed by Nintendo. The main character in Greenhouse is called "The Fumigator" in the game's manual, rather than Stanley. Their appearances also have some differences: Stanley wears overalls, but no cap, while Fumigator wears a cap and no overalls.
 * Despite being Mario's cousin Stanley never had any interaction with Mario and only made two playable video game appearances.