Who is Ezr Vinh from A Deepness in the Sky and what is their importance?

Ezr Vinh is a member of one of the families that owns interest in the Qeng Ho expedition to Arachna. He is described as a young man, who is working as an apprentice Trader when the ships reach Arachna. He is later called upon to take a leadership role after the Emergents attack and destroy the majority of the Qeng Ho fleet. Ezr discovers that Pham Nuwen is not what he appears to be, and he works to help Pham in his plan to overpower the Emergents and release the Qeng Ho from captivity.