Will and Grace should have been retitled Jack and Karen.Many shows were taken over by side characters
Fonzie in Happy Days
Alex Keaton in Family Ties
Urkle in Family Matters
Bart was the main character in the first couple seasons of the Simpsons, before Homer took the lead.
Although frasier remained the main character of his show, Niles, Marty and Daphne gave him a run for his money