Belzenlok

The elder demon Belzenlok was one of the four demons who dealt with Liliana Vess following the Mending.

History
Belzenlok fought in something called "The War of the Abyss", and had been stuck in the Abyss ever since.

The Cabal of Dominaria, desperate for leadership after the demise of The First, performed a ritual to summon Kuberr, but accidentally freed Belzenlok from the Abyss.

As part of the Cabal, the Demonlord began the process of rewriting history with himself as the lead, claiming evil titles, names, and deeds. After subjugating much of Dominaria beneath his rule, he was ultimately killed in a strike against the Cabal Stronghold by the skyship Weatherlight and its crew. The Planeswalker Gideon Jura infiltrated the Stronghold and seized control of the Blackblade, and in the ensuing battle, Liliana Vess used the legendary sword to slay Belzenlok and end his reign.

Belzenlok could (or at least claimed to be able to) smell if a person was a planeswalker or not.

Titles claimed

 * Demonlord
 * Eternal Patriarch of the Cabal
 * Evincar of the Stronghold
 * King of Urborg
 * Master of the Ebon Hand

Names and deeds claimed

 * Doom of Fools (Tevesh Szat)
 * Forger of Blackblade (Dakkon Blackblade)
 * Lord of the Wastes (Yawgmoth)
 * Scion of Darkness (Kuberr)
 * Slayer of Elder Dragons (Dakkon Blackblade)

Trivia

 * The unreleased "Salad" set (that was originally planned to be released after Dominaria) was meant to feature the giant fight against the Belzenlok and his evil forces.
 * Belzenlok's name is a reference to the biblical demon Beelzebub.