Thanks to my generous mother-in-law and her holiday largesse, I was able to order myself a copy of the Dagar The Invincible Archives Vol. 1, featuring stories by writer Don Glut and artist Jesse Santos. Should be here sometime next week.
This artwork originally graced the sixth issue of Gold Key Comics' Dagar the Invincible/Tales Of Swords & Sorcery, back in 1974, and Dark Horse Comics used it for the cover of their hardcover archive edition. Unfortunately, the Grand Comic Book Database doesn't identify the artist.