Minion of Huhetotl
Not only is he surrounded by various monsters in his temple and capable of summoning more, but he also does the "teleport away" defense, like demon lords in Gehennom and other Quest nemeses. He can inflict very large amounts of damage due to his two weapon attacks and spellcasting, so it's recommended that you teleport to the upstair after angering him and engage him there. Keep in mind that a wand of death will not work on him because he is a demon, and his high MR lets him easily resist sleep or polymorph.
Annoyingly he can cast the curse items spell - without magic resistance that can be very severe (1d6 items). You can mitigate this with the usual ways of dealing with the spell. Keep in mind that a cursed dwarvish mattock leaves you without the use of your hands. In 3.6.1, consider using a scroll of scare monster, as other melee-range spells he can cast such as drain strength and destroy armor are also particularly undesirable, and Elbereth will vanish if you melee him while standing on it.
Huehueteotl, or Huhetotl, which means Old God, was the Aztec
(classical Mesoamerican) god of fire. He is generally
associated with paternalism and one of the group classed
as the Xiuhtecuhtli complex. He is known to send his
minions to wreak havoc upon ordinary humans.