I was always curious to know why Chuck Cunningham , Ritchie's older brother simply disappeared from the show and was never referred to again. In later years it was as though there were only two Cunningham children. Can anyone tell me why?

It is one of the unsolved mysteries of TV. What happened to Chuck Cunningham....

My guess is the producers/wirters/creative folk weighed the strengths and weaknesses of the show, and Chuck was one of the weakest links. He was never around, always in class or basketball practice, so he really didn't contribute much to the show.
Originally, the show was supposed to focus on Richie and his friend Potsie and The Cunninghams, but focus was soon pulled towards Richie's pals, particularly The Fonz, Ralph and the other assorted characters at Arnold's. Plus, the show went from a filmed 50's style "Leave It To Beaver" family themed show to before a live audience 70's sitcom, so they needed strong characters to maintain a good comedic ensemble, and Chuck the always absent older college student brother just wasn't funny enough.

Or....
Maybe the guy who played Chuck got into a fight with the Producers, and they wrote his character out just to spite him.

It seems to me that two actors played Chuck. One in each of the first two seasons. If anyone knows for sure please post.

Gavin O'Herlihy played Chuck in 1974 for some episodes.
Randolph Roberts took over the role in 1974 until Chuck's unexplained disappearance in 1975.

This whole thing has X-Files written all over it!

LOL. They never did really explain it, but when they realized fonzie was so popular, they really wanted to make him into an older brother type to richie, which was no good since he had an older brother.
on the happy days biography, they said chuck was on a scholarship to the university of outter mongolia. :)

LOL. You're right. He is forgotton. I would have never thought of him again if you hadn't posted this.

I didn't think he was that strong of a character. That was most likely it.

I realize that Chuck was hardly in it! Only the first two seasons, besides Happy Days was much better w/o him in my opinion I Have An Opinion!!

As the character of Aurthur Fonzarelli was developed during the run of the show he became more and more like a big brother to Ritchie. This made Ritchie's actual big brother Chuck completely unnecessary to the storyline. Therefore for all intents and purposes Chuck ceased to exist.( or maybe he dissappeared into the Twilight Zone?!?!):happyface