Who is Messengers, a Herdsman and Pentheus's Servant from Euripides V and what is their importance?

The herdsman in "A Herdsman and Pentheus's Servantacts" acts as a messenger to tell Pentheus of the miraculous acts of the mad women on the mountainside. Pentheus' servant, in turn, acts as a messenger to tell the story of Pentheus' death at the hands of his mother and aunts.