Who is Antonio?

Sebastian wants to go to leave to go to Orsino’s court. Antonio has become close to Sebastian. He wants to follow Sebastian to Orsino's court to help him but knows that he has many enemies there. He decides that the risk is worth it to keep his friend safe.

Antonio was a sea-captain.After that shipwrecked he had taken sebastian up into his ship.Antonio conceived such a friendship for sebastian, that he resolved to accompany him wheresoever he went.On the request of Sebastian, Antonio, rather than part from him, came to Illyria, though he knew, if his person should be known there, his life would be in danger, because in a fight he had dangerously wounded the Duke's nephew.