Tsar is a toxic mage and the leader of Demon Core.
As #1 of the top 3 of Demon Core his associated atom bomb is the largest nuclear device ever detonated, the Tsar Bomba. That makes his associated country the Soviet Union, whose flag he displays on his armor.
He is the one currently dictating the course of Demon Core, swaying the others from anarchy to the organized and fanatical death cult they are now.
As a mage with a magic attribute of 7 he is slightly more powerful than Tag. He is initiated once. His patron spirit is Doom. As a so heavily corrupted mage his astral form is almost vomiting-inducingly appaling, radiating out a feeling of 'the death of all things'. He is aspected to radiation and being near it boosts his magical power.
It was him that cast the manipulation spell breaking into J4D3's dreams in Episode 12, in an attempt to turn her against Saeder-Krupp. He used fresh parts of (or the entirety of) J4D3's mother's body to link the spell. After his link was severed by Tag's counterspelling, for which 4 hits were insufficient but 8 were enough, he astrally projected and scouted out their location at the catholic community. Seeing Tag on astral overwatch, he decided not to engage.