The Nurse's role in Medea is to bring the audience into the world of the play. In the prologue of the play, she gives the historical background, provides commentary on these events, and introduces the major characters: Medea and Jason.

At the end of the Nurse's opening monologue, the Attendant enters and tells the Nurse about the rumors being spread about Medea and Jason, providing additional background for the play.

The Chorus enters, and with the voice of Medea lamenting her current woeful situation in the background, the Nurse discusses Medea's tumultuous emotional state of mind and physical decline with the Chorus.

By the time the Nurse leaves the stage, never to return, she's served her purpose (her role), which is to give the audience the information they need to understand the rest of the play.

The audience never actually sees the Nurse in her role as "nurse" to Medea. The Nurse and Medea have no scenes together. The Nurse makes only passing reference to her "princess" and her "mistress," indicating that she holds a subservient position in Medea's household, but there are only a few lines spoken by the Attendant that give any hint as to her actual role:

ATTENDANT: Thou ancient treasure of my lady's room . . .
Will our mistress be
Content, this long time to be left by thee?

As for the Nurse never returning to the play, this is not at all unusual in Greek plays. Once a character like the Nurse serves their purpose, they were never seen or heard from again.

Also, until Sophocles introduced the innovation of adding a third actor to his plays, two actors played all of the speaking characters in a play, and only two characters spoke on stage at the same time. (The Chorus usually spoke in unison, "in one voice," as a single character, although the Leader of the Chorus often spoke to other characters.)

There are never more than two characters speaking on stage at the same time in Medea, and since the Nurse had already served her purpose in the prologue, the actor playing the Nurse could play other characters through the rest of the play.

Medea's nurse functions as a kind of storyteller who helps the audience understand the background of the story; she also provides a warning about the tragedy that will later occur.

The Nurse is the first person to speak in the play. Her prologue gives the audience the background for the whole story. It explains Medea's history: how she married Jason, bore his children, turned her back on her own country, and was set aside for the daughter of Creon. It explains that she is miserable and is not listening to those who offer counsel. The Nurse says that Medea is smart and dangerous and that she's scared of what might happen.

The Nurse also foreshadows Medea's murder of her children for the audience. She says, "And she hates her children, takes no pleasure in seeing them." It's clear that Medea no longer feels motherly affection for them because her hatred for Jason is stronger than her love for the children they share.

In Euripides' Medea, which was first staged in 431 BCE in Athens, the play opens with a lamentation by Medea's nurse, who wishes that Jason and the Argonauts had never come to Colchis, Medea's native land.

Oh how I wish that ship the Argo
had never sailed off to the land of Colchis,
past the Symplegades, those dark dancing rocks
which smash boats sailing through the Hellespont.

(Ian Johnston translation)

Medea's nurse is an elderly servant who would have nursed Medea when Medea was a baby. It seems to have been common in some ancient societies for a woman other than the child's mother to nurse the child. In addition to nursing the infant child, the nurse would have remained with the child's servant as long as the nurse and the child remained alive. Compare Homer's Odyssey, where Odysseus' nurse is still alive and well in his palace after many years.

In plays like Euripides' Hippolytus, the nurse serves as a confidant for her mistress Phaedra, eventually persuading her to confess her love for her stepson Hippolytus and make an indecent proposal to the young man.

In Medea, however, the title character serves to help provide background for the play and explain Medea's current mood. Medea's nurse does not have a speaking role in the last four-fifths of the play.