One of two bosses in Necrohol of Nabudis, which you have to face if you want to get to Chaos. To get to the room with Humbaba you'll need Medallion of Courage (look in "Nabreus Deadlands" part).
About 300 000 HP
Resistant to Libra,
Vulnerable to Holy
He isn't as strong as Fury, but has more HP. Alike Fury Humbaba doesn't have variety of attacks. His attacks are: Darkness, which deals damage with Dark power to anyone in front of him and Temblor, very strong attack against the closest enemy, which (the attack) may also cause immobilize and disable. Humbaba can cast Protect on himself - dispel him right away.
In that fight use two berserked characters for short distance and one wizard for long distance. If you cannot handle it stay with one berserked character.
After defeating enemy, Lusterless Medallion gets a shot of power (it becomes Medallion of Might if you defeated Fury earlier). You will also obtain Necrohol of Nabudis map.
You'll get 2100 gil from Montblanc as a reward