Who's This? Donald "Dan" Richards was chronologically the first Manhunter, as shown in Who's Who vol.XIV, page 18.
How you could have heard of him: Seeing as he's a Manhunter, it was almost inevitable that he'd feature in Millennium (where it was decided his dog was a robot Manhunter agent), in that book's second issue Infinity Inc. #46-47 (and 52), and in the Millennium-centric Secret Origins #22. Roy Thomas also used him in All-Star Squadron and Young All-Stars a number of times. Most recently, he's appeared in Marc Andreyko's Manhunter series where Kate Spencer's son inherited Thor the robot dog! He was killed by Mark Shaw (Manhunter III) using the Dumas persona.
Example story: Police Comics #17 (1943)
So what this old Manhunter strip any good? Well, I wouldn't call it amazing, but it had shocking Golden Age violence and dynamic fight scenes. And a crime-fighting dog. Let's not forget this same issue would also have given you Plastic Man, the Human Bomb, Destiny and Phantom Lady!
Who else? There's an awful lot of sword&sorcery half-pagers in this volume - Malagigi, Mara, Mariah - but I've no interest in covering them at this juncture. No, next up, I think, is a Bronze Age villain that never got a post-Crisis shot.