Howard Browne
The Return of Tharn
1948 (1956)
from the dustjacket:

The fantastic adventures of Tharn, the fabulous "Warrior of the Dawn," are once again available in a second book from the pen of popular Howard Browne.

Tharn's existence dates back to 1943, when "Warrior of the Dawn," the first novel of the series appeared as a long book. This sequel, complete in itself, takes up the thread of excitement in no less of a swashbuckling manner.

Tharn is a Cro-Magnon — a true man of the dawn age, dating back to the morning of time on this planet. His adventures are decidedly fantastic, leading him through savage jungle to the barbaric kingdom of Ammad, majestic and intriguing in all its forgotten might.