Who is he ?

Lucentio’s servant. Tranio accompanies Lucentio from Pisa. Wry and comical, he plays an important part in his master’s charade—he assumes Lucentio’s identity and bargains with Baptista for Bianca’s hand. Tranio is Lucentio's "trusty" servant. Unlike the other servants, Tranio is smart, loyal, and acts as a kind of surrogate father or mentor to Lucentio. He gives all kinds of advice like "Forget studying, you should really meet some girls while you're in Padua" and "Hey, why don't you impersonate a teacher so you can get close to Bianca?" Tranio is also really indulgent (sort of like Juliet's nurse in Romeo and Juliet) and agrees to traipse around town pretending to be Lucentio so that the real Lucentio can run around as the tutor "Cambio" while he pursues Bianca.
taming of the shrew- act 1 scene 1