Madman

Madmen are hostile creatures in Desolate. They are seen all over Granichny. Madman are easily spotted since their eyes glow and they mumble constantly. Occasionally, Madmen will be seen banging their heads against walls. They usually swipe at the player with their bare hands, though some occasionally carry torches, especially at night. These can set the player on fire, forcing them to stop fighting or else take continuous damage.

Upon death, Madmen drop a variety of items, and will always drop Cloth.

When in combat or near a madman, the player's sanity will drain.

At research rank one, stress gained from combat or being near a madman is reduced by 30%

Developers description
Before the event, “Madmen” used to be regular people living their lives on Granichny - now they’re nothing but rambling shadows of their former shelves. One of the United Republic of Soviets’ most popular scientific publications, “The Saturn”, described their altered state as “a kind of mental fissure”. To be more precise - something new entered their being, and remained there. Something alien.

Despite being quite a nimble and tricky foe to fight, a single madman is not that threatening. However, if you alert him of to your presence - Madman yells and growls will instantly attract more of their kind.

There is some evidence these were in fact people experimented on if the prologue is to be believed.