There's two recent books from Dark Horse that collect the entire Solomon Kane run of stories previously published by Marvel.
One is titled THE SAGA OF SOLOMON KANE, that collects all the stories that appeared in black-and-white Marvel magazines, spanning a 20-year period. About 60% are Robert E. Howard story adaptations, with a few new/original stories. Plus dozens of beautiful pin-up pages, including this one by Wrightson. A tremendous collection of artistic talents drawing the character: Gene Day, Ralph Reese, Al Weiss, Neal Adams, Pablo Marcos, Mike Zeck, Howard Chaykin, Sonny Trinidad, Rudy Nebres, David Wenzel, Dan Bulanadi, Steve Carr, Al Williamson, Colin MacNeil, Jim Fletcher, Bob Gould, John Buscema, John Byrne. And Wrightson. Ranging from pin-ups to full stories, but nicely interpreted, either way.
A second thinner volume, CHRONICLES OF SOLOMON KANE, collects all the color Solomon Kane stories done for Marvel, a 1976 two-issue Thomas/Chaykin story done in MARVEL PREMIERE 33 and 34 (adapting Howard's "Red Shadows"), and a six-issue 1985 miniseries, 4 of which are Howard adaptations.
Between the two volumes, they adapt 13 of the 16 Howard stories, some of them adapted twice, by different hands. 4 of the 16 are incomplete story fragments by Howard, one loosely adapted and expanded on freely, the others not adapted. Two of the four Howard fragments were expanded and adapted in separate new books by Dark Horse, CASTLE OF THE DEVIL, and DEATH'S BLACK RIDERS about 10 years ago, that I found not overly satisfying reading. The first at least had very ornate art.
I liked the Howard fragment stories better in a Robert E. Howard text paperback edited by Ramsey Campbell, collecting all 16 Howard stories, I think for the first time (1995), where Campbell I thought did a far superior job of expanding them into full stories that were good reading.
