Dominions 3: The Awakening/Mictlan/Mictlipoctli

Commentary
Possibly the only hero available to Mictlan in the Early Era, Mictlipoctl offers an excellent way to "bootstrap" yourself to a sizable undead force:

Research to Blood-5, and have him cast Contact Civateteo at the relatively low cost of 25 blood slaves. The Civateteo can then start to reanimate (as can Mictlipoctl himself).

A few turns this and you can get quite a factory of Civateteos churning out decent-sized armies of undead legions quite quickly.