Kathok, Roar of Xol
From Destinypedia, the Destiny wiki
Kathok will continuously bombard the player's position with highly-damaging explosive Arc bolts fired from his Boomer, and will use a Fist of Darkness at close range to knock Guardians back a significant distance. He will constantly be backed by lesser Hive reinforcements as well as Shriekers, and will be surrounded by an immunity shield that can only be shut down by Cleavers that are obtained by killing Severing Knights. Once Kathok's shield breaks, he is vulnerable to all damage for a brief period.