The Hades Legionnaire is an Underworld version of the Legionnaire Captain. It appears similar, except it is wreathed in hellish flames. It's also just as powerful, and it fights the same way. Kratos can also damage and kill it the same way he damages and kills a Legionnaire Captain.
In God of War, Kratos encounters these deadly warriors in packs as he traverses the Path of Hades to escape the Underworld.
In God of War II, he battles three of these fiends as he climbs Atlas, and they also appear as he makes his way through the Phoenix Chamber.