A party to dress up as a cartoon character, host is Robin

Who or what am i?

Nellie the elephant plays her part
She's right in the middle, but not at the start
Oor Wullie is needed, but not a whole lot
'Oor', can help, but 'Wullie' cannot

Neither Popeye nor Brutus is needed to play
But Olive Oil is here to stay
Indiana and his quest for treasure
Must be involved, just for good measure

If Humpty Dumpty can stay in one piece
Hel'll keep me together, last but not least
Bill could be there, or perhaps even Ben
But I only need one of the flowerpot men

If Rumpilstiltskin plays his fiddle
You'll have all you need to solve the riddle

One final clue to help you along
But be careful, or you'll get it all wrong
The answer is easier than it first may seem
I fit right into this party theme