Detos are demonic soldiers that appear in Leningrad.
They don't have a ranged, or a melee attack, and have quite high health. Their only attack is rushing toward player and detonating themselves, dealing huge amount of damage. However they can be easily stopped with secondary fire of the Shotgun, and destroyed into icy pieces. Luckily, there are few of them in whole level.
According to his uniform, he is Russian.