Brother Karel, Ancient Nephalem Guardian is a Super Unique Skeletal Shieldbearer, an ancient warrior guarding the Drowned Temple in Diablo III. The player has to fight him, along with Brother Moek and Brother Larel. They all spawn once Ezek the Prophet is defeated, and killing them opens the path to the Sword Shard.
In combat, Brother Karel has a Knockback affix.
Brother Karel's name may be a reference to Joachim Karel from Tomb Raider: the Angel of Darkness. In that entry of the Tomb Raider series, he was revealed to be a Nephilim.