Who is Pham Nuwen from A Deepness in the Sky and what is their importance?

Pham Nuwen is an imposter, posing as Pham Trilini. He is a Programmer-at-Arms of the Qeng Ho, and although, he is viewed as a bumbling old guy with few responsibilities and little skill or talent.... he's essentially the man responsible for founding the Qeng Ho as a trading nation.