Poof Fairywinkle Cosma is the baby of Cosmo and Wanda, whose most notable spoken word is "Poof."
The first season that Poof appeared, he was mostly like a baby: dependent, relying on Cosmo, Wanda, and Timmy for everything; and crying all the time. By the time of Wishology however, Poof was starting to do more, such as dressing up as a ninja, fighting and defeating The Eliminators. By the next season, Poof's magical abilities have improved to the point where he can grant wishes, sometimes even if Timmy doesn't really want them granted. Poof got himself in a myriad of adventures this time, including catching the Chicken Poofs and turning everyone in Dimmsdale into chickens, taking a trip to Yugopotamia, and helping Timmy Turner and his team the Dimmsdale Victims win their way to the soccer championship. Interesting enough, in the latter example Poof was able to do so without interfering with Da Rules, meaning Poof might possibly be able to grant wishes that Da Rules do not allow.
Poof has an Anti-Fairy counterpart that was born to Anti-Wanda during the TV special, Anti-Poof. Because Anti-Fairies are opposites of Fairies, it was the female who gave birth this time around. When Foop was born, he could already speak and had stereotypical evil villain facial hair. Poof and Foop eventually battled with each other, and Foop was defeated and locked in Abracatraz.
Around the end of Season 7, Poof began to attend Spellementary School, a pre-school for magical creatures where they learn how to control their magic powers. Poof's teacher is a friendly fairy woman named Mrs. Powers, and all of Poof's classmates adore him with the exception of Foop, who is also attending and constantly competing with Poof for attention.
Poof and Timmy
Timmy has been entrusted by Cosmo and Wanda in taking care of Poof whenever they are away. Usually Timmy's carelessness results Poof being put in "danger", although it is usually Timmy the one that is endangered by Poof's wandering. Timmy is responsible for Poof's existence by wishing for him.
Poof and His Parents
Wanda is usually the one taking care of Poof and tending to his needs. Cosmo also has a hand in parenting in the episode "Playdate of Doom", but otherwise is admittedly bad at parenting because he never went to school for it. Many times when Poof is put in danger, Wanda will start to panic.
Poof and Goldie Goldenglow
Poof will be getting a love interest in the upcoming special "Love Triangle". This baby fairy is a girl with blonde hair that Poof and Foop immediately fall in love with.
Poof and Foop
Although Poof and Foop are mortal enemies and complete opposites, they also attend the same school together and, before Goldie Goldenglow's arrival, appear to had even been developing a friendship.