Since nobody else answered your question I will. Tyrant is the original creation of Galactus. Tyrant was never a herald, Galactus created him to be a near equal companion. Tyrant however decided he wanted to rule the Universe while Galactus wanted only the worlds he needed to sustain himself. Galactus decided Tyrant's plans would create Universal chaos and thus a horrific battle ensued between the two where several galaxies were destroyed, and Galactus emerged victorious.