I recently read The Saga of King Kull by Robert E Howard. It was a collection of 1 poem and 3 short stories, about 90 pages total (e-book pages, whatever that translates to on paper). Published in Warsaw, Poland, but in English.
The poem is The King And The Oak and the three stories are The Shadow Kingdom, The Mirrors Of Tuzun Thune, and Kings Of The Night. The stories evolve from sword-and-sorcery to historical fiction/time travel. Howard uses names of fictional and real groups of people: Kull is an Atlantean who has taken the kingship of Valusia, but he meets Picts, Britons, Danes, and Romans.
Howard uses some of the same tropes as Conan - temples of serpents, shapeshifters, Kull is a noble barbarian in a decadent older society, etc. I also saw some similarities to Moorcock's Eternal Champion. The Mirrors of Tuzun Thune had a little Jack Vance feel to it as well.
The King Kull stories are really interesting precursors to Conan. Although there are some common themes, the two characters are quite different, and the way Howard wrote their stories reflects this. Kull tends to be more introspective and thoughtful than the more instinctive and active (dare I say virile) Conan.
The most interesting comparison, which you may or may not know, is that the first Conan story, The Phoenix on the Sword, was re-written from a rejected Kull story, By This Axe I Rule!.
It would be great to get some Kull on Elder Sign in the future. I think The Mirrors of Tuzun Thune in particular would be a good fit.