Nephews to Donald Duck, grandnewphews to "Uncle" Scrooge McDuck. Donald's sister left them on his doorstep to be babysat one day, and Donald's life was never the same again.
The triplets were horrendously mischevous and they loved to get a reaction out of their famously tempermental uncle. This was not hard to do.
Donald loved his nephews, though, and although he often lost his temper, he never gave up trying to get through to them. As they matured, they mellowed a bit, and while they still enjoyed playing tricks on Donald, they were much more creative and less destructive about it.
Eventually, Donald decided to enlist in the Navy. Perhaps he had grown tired of people questioning why he wore that sailor suit if he hadn't ever been in the Navy. Anyway, he dropped Huey, Dewey, and Louie off at their Uncle Scrooge's mansion.
Scrooge was not pleased, but the triplets quickly grew on him. Their extensive knowledge of wilderness survival techniques, obtained by their membership in the Junior Woodchucks, was often indispensible to him on his many journeys around the world. And the boys loved to go out on adventures with their great uncle. These adventures were chronicled in the TV series DuckTales.
Donald's tour of duty in the Navy didn't last forever. The next time we heard of the triplets, they were again under his custodianship, and had aged significantly. Now teenagers, they once again resumed their propensity for pranks, particularly directed toward their "Unca" Donald. They often accompanied Donald as he worked as cameraman for Daisy, who was a television news reporter. These stories were recounted in the TV series Quack Pack.
The triplets started out nearly identical. Occasionally, they would be seen wearing different colors, but they were still of a single mind -- so much so that sometimes, a single sentence would be distributed among the three of them, as if they were simply three bills on the same duck.
Only in DuckTales did they begin to differentiate. They were also each assigned a particular color.
These personality traits were very subtle, and often not strictly adhered to, but occassional glimpses of consistency were observable.
In Quack Pack, the triplets have become fully separate ducks, each with his own style of dress, speech, and hair, and with the personalities explored even more deeply.