My favorite character was Reject the Robot

I beg to differ with MovieChat's description -- Johnny Jupiter wasn't a puppet, he was a Martian or something. But when the store clerk communicated with him over his two-way interplanetary television (which he kept in the back room of the store), Johnny was (very obviously) played by a puppet, so he'd fit on the "TV screen."

In real life, of course, Johnny was much larger, or at least I assume he was, because I distinctly remember another character, Reject the Robot, being played by a puppet when he appeared on the same TV, but when he travelled to Earth and walked into the store, he was apparently played by a guy wearing a costume made from cardboard covered with tinfoil. I liked Reject so much that a few years after the show went off the air, I thought its title had been "Reject the Robot" (till my mother corrected me).

We also saw a third character on the TV. He was Major Domo, apparently a military fellow, though all I recall is his name. (I had no idea at the time that his name was sort of a pun.)

I also recall that the show was sponsored by M&Ms, and Wright King (who played the store clerk) would do the commercials in character, right there on the store set (the candy counter sold M&Ms, of course). He had a very generously-sized mouth, so that when he said M&Ms "melt in your mouth," I was impressed!