The Marvel version of the character didn't exactly lift the character out of obscurity, being a well known figure among sword and sorcery fans even then due to the efforts of L Sprague De Camp. However, it certainly broadened his audience and introduced him to a new generation of readers. It also permanently changed the mythos of the character by introducing the chainmail bikini version of Red Sonja.
Roy Thomas was commissioned to do a bunch of articles for a Spanish magazine on his work creating Conan the Barbarian that somehow spiralled out of control into talking about every single issue of the 100+ issue saga. When asked to do an English language version, he just pulled out all his untranslated notes and spruced them up into a three volume book set. In this case, Roy talks about the first fifty-one issues of Conan the Barbarian as well as the fascinating story about how he managed to get the rights to the character for $200.
Honestly, this book needs to probably be read with the purchase of volumes 1-4 of CONAN THE BARBARIAN THE MARVEL YEARS EPIC COLLECTION. It basically reads like the annotations to those four volumes, especially for someone who didn't collect the original works. Now if that seems like a rather significant monetary investment for you, well, it is, but I have to say it's been an incredibly fun month of reading issue by issue then consulting Roy Thomas' notes on them.
Even without Roy's meticulous notes and eidetic memory about the process of creating Conan the Barbarian, you have a fantastic collection of stories from a man who manages to make the process of editing comic books seem like the funnest job in the world. Roy is an avuncular guy and seemingly has no end of stories regarding his struggles with the Comic Book Code Authority (that objected to the fact Conan is a womanizing thief and murderer for some reason) as well as his deep friendship with various artists.
Roy became a fan of Robert E. Howard's Conan the Barbarian only after he tried and failed to get Thongor the Barbarian's rights. He loved the character so much that he did a decent job of trying to adapt all of Robert E. Howard's stories in chronological order and maintain continuity with the L. Sprague De Camp literary timeline of the Barbarian's life. Something Roy notes that he disagreed with several elements of in the way only true competing nerds can.
Conan is the kind of character that worked very well in Marvel comics hands and Roy was used to working with other people's properties. His original content may not be Howardian but it was fun reading this guy talk about Wolverine and Stan Lee's dislike of fantasy before wandering off into discussion of the Trojan War as well as the ballad of Cu Chullainn. We also get his insights into the creation of Red Sonja from Sonya of Rogatino as well as the mythological inspirations for her "no man shall bed me unless he bests me in battle." Which Roy, with no hesitation, admits he got literally decades of heat over from male and female fans alike.
In conclusion, this is one of my all time favorite nonfiction supplements to Marvel comics. It provides an endless amount of insights into the culture of that company in the Seventies, fantasy fiction at that time, as well as Conan the Cimmerian before he became quite the pop culture icon that he is today and was still mostly known by sword and sorcery die-hards. We even have the story of how Roy Thomas got Michael Moorcock to write a two-issue story about how Conan met Elric.