Cartoonist Russell Myers has been formally recognized by the Guinness Book of World Records for the "Longest running daily cartoon strip by a single author." This is for producing the Broom-Hilda newspaper strip since April 19, 1970 — a feat which I believe was called to the world's attention by this blog back in this message.
It seems unlikely anyone will wrest the title away from him in the few decades. I don't know who the next contender would be but Russell ain't stopping now. And even if he quit or died tomorrow, he still has a year or two of Broom-Hilda strips in inventory.
Speaking of dead cartoonists: The Guinness folks currently recognize Johnny Hart as the "Most syndicated living cartoonist" and their listing says…
Johnny Hart, creator of The Wizard of Id and B.C., is the most syndicated living cartoonist with both these cartoons syndicated in 1,300 newspapers each, giving his work a combined total of 2,600 syndicated outlets.
I don't think this was ever a valid record because, first of all, the way syndicates count newspaper strip placements involves counting daily strips and Sunday strips as two separate sales. If the Picayune Post-Dispatch carries a strip seven days a week, the syndicate counts that as two newspapers, not one. One newspaper that carried B.C. and The Wizard of Id both daily and Sunday would be considered four newspapers. So the total number of papers carrying Hart's two strips has really always been way less than 2,600.
Secondly, I believe Charles Schulz and Jim Davis, creators of Peanuts and Garfield respectively, have both at times appeared in more newspapers with one strip apiece than Johnny Hart has with two. Of course, Charles Schulz no longer qualifies as a "living cartoonist"…
…and since his death in 2007, neither does Johnny Hart.