Tim, since you asked here are a few links (1, 2, 3) re: J C Coll. I was introduced to this phenomenal artist by another awesome artist, Al Williamson. He gifted me "The Magic Pen of Joseph Clement Coll" while I was a student of his at The Joe Kubert School of Cartoon and Graphic art in the mid 80s. This book has been an inspiration to me for nearly 40 years.
He influenced Frazetta, Williamson, Stout, Krenkle and so many more. His work sparked imaginations and brought a level of believability to the fantastic stories that populated the newpapers and popular publications of the time. He died at the age of 41 and one can only wonder what he could have accomplished had he lived to a ripe old age.
A bit of his technique...
... and an unfinished piece to get an idea of how he worked. This is actually quite large and it was hanging in Al Williamson's kitchen back in the day. I wish I could study it more closely now but, alas, I have no idea where it resides.
Do an image search for Coll, it'll blow your mind. And just for good measure, another that could have been Shiwan Khan.