After scouring the internet and coming up with nothing, I finally found the answer in the most unlikeliest of places: my aunt’s house. There, by complete coincidence, I saw this keychain:
My aunt says it’s from a pencil case she bought at Borders books, a pencil case like this:
Which has this keychain:
Look a little familiar?
Thanks to this, I was able ...
That would be the Power Lords series of toys by Revell. There was a comic run, even a video game, but never any cartoon associated with them. The particular character you describe is the main one, Adam Power.
The main female character Shaya is somewhat disturbing, as her alternate form looks like something that escaped from a horror movie.
That figure sounds like Matt Mason and this link confirms there was a tie-in book with moon worms:
The writing is iffy at best but wildly, and I mean WILDLY imaginative:
moon rabbits, moon worms, "nothing" beings--and all the great Major
Matt Mason vehicles.
It appears to have been a Whitman Big Little Book, and is listed on a collector's info page ...
Orphaned American boy Joey lives with his grandmother, working at a restaurant in the West Coast city of Center City (センターシティ Sentā Shiti, based on Los Angeles), while going to school. Upon hearing of a new toy robot called the Heybo, Joey believes that getting one will make his life better, turning him into a hero to protect his friends and ...