The thermonuclear smoke devil, often referred to as thermy, is the boss version of the smoke devil. It requires a minimum of 93 Slayer to damage. Located at the Smoke Devil Dungeon south of Castle Wars, the Thermonuclear smoke devil can only be attacked on a smoke devil task, with the exception of one kill for the Western Provinces Diary (provided that the player has 93 Slayer without boosting).

It is the only monster to drop the smoke battlestaff, jar of smoke and the pet smoke devil. It drops the occult necklace at a higher rate than smoke devils do.

Unlike most NPCs, the Thermonuclear smoke devil is always able to walk through other monsters/players. This is to prevent players from safespotting the boss using the smoke devils found in its lair.

A dwarf multicannon cannot be used inside the boss room. If it is set up, the cannon will be destroyed (as in the lairs of the KBD and KQ).