Thirteen such men have been known to exist in canon, as well as a small number of quasi-Zoalords - such as Griselda and Masaki Murakami. The most prominent Zoalords are those that make up Chronos' Council of Twelve.
Every Zoalord seems to have the power to manipulate gravity and radiant energy to some greater or lesser extent, as well as to create a barrier-shield, to fire beams of destructive energy from their forehead-mounted Zoacrystal, and to command lesser Zoaforms.
The Zoalords seen thus far in the Guyver series are Alkanphel, Hamilcal Balkus, Li Yentsui, Edward Caerleon, Jabir Ibn Hayyan, Richard Guyot, Waferdanos, Shin Rubeo Amniculos, Tuaha De Galenos, Kablarl Khan, Luggnagg de Krumeggnik, Imakarum Mirabilis and Fried'rich van Purg'stall.
Zoalords in Warrior Guyver
Zoalords in Son of Mine ('verse)
This series has thus far introduced one new Zoalord: Imakarum's son Ingriam Mirabilis. The powers of this, the youngest of Chronos' Zoalords to date, are mostly imitations of his father, the Zoalord of Gravity. However, after he is given the Zoacrystal of Luggnagg de Krumeggnik, he gains the secondary power to manipulate wind currents.