Depending on whether the thaumaturgist was good, evil, lawful, or chaotic, the beings that the thaumaturgist could summon varied. The beings could range from demons to devils, and from angels, to eladrin. The nature of the relationship between the thaumaturgists and the planar creatures may also have varied depending on the duties the thaumaturgists wished the planar creature to perform.
Thaumaturgists oftentimes formed a long-term relationship with specific summoned fiends or celestials, who were called "planar cohorts." These relationships were chiefly dependent on the thaumaturgist and their planar cohort sharing the same basic goals and motivations. Should this situation change, the planar cohort was not obliged to remain on the Prime Material Plane.
Thaumaturgists were very skilled and persuasive at getting their planar allies to work for them at considerable discounts. Thaumaturgists possessed such skill and power at summoning planar allies that they had enhanced physical strength and stamina. Skilled thaumaturgists' summoned planar allies remained twice as long on the Prime Material Plane than they usually would.
Thaumaturgists could ready a summoning spell to "fire" when a prearranged condition was met. These skilled casters could enter into long term business relationships with summoned fiends or celestials. As long as the thaumaturgist assisted the summoned planar creature in a cause or ideal it believed important, the planar ally would remain to assist.