Even before Vertigo was Vertigo, it had a distinct policy of signing great cover artists for the long haul for ongoing titles. I fondly remember Dave McKean on The Sandman and Hellblazer, Simon Bisley on Doom Patrol, Brian Bolland on Animal Man and Brendan McCarthy on Shade, the Changing Man. This is a policy that has continued on to the present day: Yuko Shimizu has produced amazing covers for The Unwritten since its debut; king of the good girl artists Adam Hughes has been providing Fairest with the best work of his career so far; and Fables had a long outstanding run by James Jean, before he ceded the job to Joao Ruas. As much as I love the work of J.H. Williams III, it was seeing McKean's cover for The Sandman: Overture #1 that made the project feel real.
In terms of total commitment to a book, however, no one can match Dave Johnson on 100 Bullets. He drew covers to all 100 issues, shifting styles for each story arc. He drew the covers to all 13 trade paperbacks, and now he's providing the ones for the eight-issue sequel-of-sorts Brother Lono. On Tuesday he posted this image to his assorted social media feeds: the covers to the five omnibus editions, which together create an extended frieze.
"Finally finished the last (5th) of the 100 Bullets Omnibus edition covers. Here they are all connected. It's funny that I didn't lay this out all at the same time. I had an idea in my head, but I did them one at a time. Kinda like an Exquisite Corpse style. Glad it all worked out."
Of course, when Brother Lono is finished, there will be a trade paperback cover to draw. And then, who knows how many of the other survivors of 100 Bullets #100 have their own stories to be told? Johnson could be continuing to work on these characters for a long time to come.