Who is Old Man (from Electra) from Euripides V and what is their importance?

The old man was once the servant of Electra's father, Agamemnon. When Orestes was a little boy, he saved Orestes from Agamemnon's murderer and usurper, Aegisthus. The old man is the only one who recognizes Orestes when he returns to Argos in disguise.