Sparky is a hyperactive fairy dog that becomes Timmy Turner's pet. He first appeared in the episode "Fairly OddPet". He was adopted by Timmy, who wanted a dog after realizing everyone in Dimmsdale had a pet but him, but as he was banned from all the pet stores of the town, he had to adopt a dog from Fairy World.
Sparky has yellow fur, except on his ears and the top of his head, that are orange. He has blue eyes and a star on his tail, which he uses as a wand. His character is modeled after Rick Moranis'Louis Tully character in "Ghostbusters" - a hangdog, hard-luck type who means well but is kind of a doofus.
Sparky is a cheerful fairy dog but is troubled, due to most of the people who adopt him being forced to take him back due to his craziness. He claims he is just doing "dog things" by chewing and digging and running around, sometimes causing trouble for both his owner(s) and others, such as their family members and the people that live in the same town. He sometimes leaves a nasty surprise for his owner(s) overnight because apparently fairy dogs do not sleep and he just does those "dog things", as mentioned earlier.
Being a fairy dog, Sparky can do magic just as any other fairy, and uses his tailwand to do so. However, instead of world-changing magic in line with the chaotic wishmastering of Cosmo and Wanda, Sparky possesses "dog magic," allowing him to conjure up bones, fire hydrants, and the like. Some of his misadventures include afflicting Timmy's hometown with magical fleas (Fairly OddPet) and wishing himself into a real boy (out of jealousy that kids seem to get all of the attention). According to show's creator Butch Hartman, "He doesn't really add much magic-wise, but he does add a lot character-wise."
The addition of Sparky to the show was first announced on July 14, 2012, in the San Diego Comic-Con, during "Butt Biting and Magical Mischief!" panel, dedicated to Butch Hartman’s two shows on Nickelodeon, "T.U.F.F Puppy" and The Fairly OddParents. 
During the panel it was also revealed the dog's first artwork, however, in the picture, Sparky was colored blue and purple, instead of the yellow and orange coloration he has in the actual episodes.
"Fairly OddPet" premiered on March 23, 2013, introducing Sparky. In the episode Timmy Turner decides he must have a dog, as he realizes he's the only one in Dimmsdale that doesn't own a pet. After he gets his parents permission to have a dog, he wishes to be in the pet store, but Wanda poofs him into the Fairy World Pet Store, claiming he was banned from all the regular pet stores. There, he adopts Sparky after getting marveled by the fact of he being a talking dog.
During the episode Sparky shows to be a lot of trouble, to the point Timmy decides he must give him up, but later, when Sparky hears Timmy's plan to abandon him and leaves, he ends up in danger and Timmy risks his own life to save him, showing that both love each other, and Timmy decides to keep him as his pet.
Hartman explained that he loves to add characters to "The Fairly OddParents" because it really expands the show. "Timmy Turner loves animals, I obviously love animals and we don't have magical animals on the show.", he said about the addition of Sparky.
In "Fairly OddPet" it's said that he was brought back to the Pet Store 83 times before Timmy adopted him, as his previous owners couldn't handle all the problems his crazy behavior caused. No matter where it's gone or what is done, Sparky's either been there or done that or knows a guy who's done it, for example, when Wanda suggested moving to Mexico , he mentioned having known a guy there who could "set them up" (I Dream of Cosmo).
Timmy is the character Sparky interacted the most with until now. Timmy is Sparky's owner and the person Sparky loves the most. In "Fairly OddPet" Timmy decides to give Sparky away after he starts causing too much trouble, but after feeling bad about the dog's heart-break, Timmy ends up risking his life to save Sparky, letting clear they both love each other.
Being a current member of the main cast of the show, Sparky is seen aside of Timmy's Godparents in every episode after "Fairly OddPet", however, to date, he hasn't had any kind of deep interaction with Cosmo, Wanda or Poof, and haven't even said anything that showed his thoughts about them.