Solid Jackson is a friend of Natch Kilroy, and another funny character from The Kilroys, a popular teenage series from ACG in the late forties and early fifties. Animator Bob Wickersham (“Wick”) did the artwork and Hubie Karp wrote the story.
The phrase, “Solid, Jackson!” was in use during the war years based on this photo.
After the war it was used in hipster-talk. Man, if everything is aw reet, copacetic, then you is solid, Jackson! I’m glad to see that according to the Urban Dictionary the term is still being used, but in reading their definition, maybe more graphically defined than 65 years ago.