Le Beau is a critical member of the cast in Act II, Scene II who exits the play at the end of Scene II. He introduces several events and ideas that are essential to understanding the unfolding of the play. He is a minor courtier in Duke Frederick's court who is noted as a bearer of unofficial court news (gossip, if you will):
With his mouth full of news.
Which he will put on us, as pigeons feed their young.
In his capacity as news-bearer, Le Beau introduces the wrestling match between Charles and Orlando by telling Celia and Rosalind about it. Celia is not interested but Rosalind responds with feelings of intrigue. Thus Le Beau gives Rosalind opportunity to reveal an important part of her nature and a big difference between Celia and Rosalind (Celia later reveals an important character trait of her own when she acquiesces to Rosalind's interest in seeing the wrestling match).
After the match, Le Beau fills a couple of other important functions. He informs Duke Frederick that Charles is injured to such an extent that he cannot speak, and he warns Orlando to immediately leave because the Duke is in an uproar over Charles injuries. Le Beau also gives important information about Celia's and Rosalind's temperaments, saying neither are like the Duke, and about their loving relationship and about the Duke's feelings toward Rosalind: he is displeased with Rosalind because the people praise her virtue and pity her deposed, banished and exiled father.
Le Beau ends his role by predicting that at any time the Duke's ill-will could erupt against Rosalind (" his malice 'gainst the lady / Will suddenly break forth"), which is important information for understanding the Duke's upcoming rejection of Rosalind in Act I, Scene III:
Mistress, dispatch you with your safest haste
And get you from our court.