Al Williamson was a big fan of Alex Raymond's Flash Gordon comic strip back when he was a boy, and the obvious influence of that work led his career to intersect with the character multiple times in the last half-century. All of the major intersections, as well as many minor ones, are collected in the gorgeous volume AL WILLIAMSON’S FLASH GORDON: A LIFELONG VISION OF THE HEROIC from Flesk Publications, a large 9x12 256-page book published last year.
The majority of the artwork in the book is presented, whenever available, directly from Williamson's original artwork, which is a treat no matter what the subject matter, but especially so on work that he lavished so much detail on.
While there were a few earlier bits, a short stint assisting on the comic strip in the 1950s and much unpublished artwork just done for fun, Williamson's first major work on the feature was the comic book published by King Features in the 1960s. He only did three issues (1, 4-5) before other more lucrative work called, but they're really good issues. Williamson writes some of the stories himself, with Larry Ivie and one of his most frequent collaborators Archie Goodwin doing some of the writing as well, and they're decent classic adventures taking our characters to exotic hidden locales and facing danger. They're definitely the highlight of the book, especially the excellent reproduction when the original artwork was available (and the few pages where it seems it wasn't are pretty well printed, too).
A while after that there was a little oddity, a series of advertisements for Union Carbide using the cast of Flash Gordon to sell their Bakelite plastics. The odd concept only grows more distasteful with the subsequent history of the company, and as you can see the product placement is done with no subtlety at all. I'm sure after enough of Flash's shilling for Union Carbide and a few industrial accidents the residents of Mongo were ready to welcome back Ming the Merciless. At least you know where you stand with Ming... Still, if you ignore the words entirely the artwork is as excellent as you'd expect.
As much as we might like to forget, there was a movie version of Flash Gordon in 1980. Fortunately, it did lead to a comic book adaptation drawn by Williamson (with script by Bruce Jones and a few other artists assisting). I haven't seen the movie since it came out, and it's renowned for some awful dialogue. A quick check of the IMDB entry for the movie shows Jones wisely used very little of the worst excesses. The story as presented here is very choppy, but Williamson's artwork makes it worth looking at, while making you wish he was allowed to just be himself on a lot of the character and setting designs. Also of note, because the artwork was prepared to be used in many formats, a lot of the stuff on the edges of each page wasn't as widely seen (cut off entirely in the comic book version, cropped off slightly in the full-bleed album version), and those lavish designs are often the best part of the page.
While Williamson has worked primarily as an inker since the mid-1980s, one major return to full art was again for Flash Gordon, this time a 2-issue series written by Mark Schultz and published by Marvel in 1994. A fun little adventure taking Flash through many of Mongo's scenic attractions, worth having in this version even if you have the original comics thanks to the great reproduction and the restoration of some dialogue changes made in the published comic.
There's a lot more besides that in the book. Williamson frequently drew Flash Gordon for amateur publications, or for special projects, or sometimes apparently just for his own amusement. He also did a few guest spots on the comic strip during Jim Keefe's tenure as artist. And there were pages from the movie adaptation unfinished and unused as script changes were made. This book presents all that stuff and more, as well as extensive text by Mark Schultz on the background of Williamson, Flash Gordon and each individual project.
Highly recommended if you like Williamson or Flash Gordon.