Bir-T-der was a Kig-Yar sniper serving in the Covenant. When the Great Schism was enacted, he, Tir-D-yar and Yir-T-sar escaped High Charity. They later served themselves until hired by Beracus to assassinate the Sangheili Stel 'Vadam. After the deaths of Tir's brother and Yir, only Bur and Tir lived to escape Doisac. However, he was corned alongside Tir by Stel 'Vadam and his group. Pretending to be Tir, he quickly knocked out Ral 'Daman, defeated Doug-103 and killed Rochelle-108 (using a Plasma Charge given by Tir to assist him). However, he was later decapitated by Stel 'Vadam in an act of vengeance. Tir-D-yar later recovered Bur's skull. What became of his skull is unknown, as it hasn't made an appearance in Halo: Sangheili Brothers or Reach, it was likely destroyed during Tir's travels by the Sangheili, although it could still be around.