Well, according to the All Knowing Google:
"Maynard lived in his own world with its own twisted logic. His name was also illogical, the "G" stood for Walter. According to the show's creator, Maynard was named after his Aunt Walter who was married to his Uncle Edith. His speech was full of colorful phrases such as "You rang?" and "Like, I'm getting all misty". But Maynard G. Krebs will always be best remembered for his response whenever anyone mentioned the subject of work. He would instantaneously shudder, and let out a plaintiff cry of "WORK!?!?"
(I just cut and paste these things, so I take no credit for the All Knowing Google's referring me to a page that doesn't know the difference between 'plaintiff', a noun, and the adjective, 'plaintive').
But one can see here the answer to all three points: George's objection to that four-letter word and what the word was; Steve'nEllen's, "G stands for Walter??"; and all the youngsters out there wondering, "Who the H is Maynard G. Krebs?"