In linguistics and grammar, a pronoun is a pro-form that substitutes for a noun or a noun phrase. Some of these pronouns have developed along the development of the English language period, having different significant in each period. Such is the case of the pronoun you, which developed from þū on old English to you in modern English.
On the other hand, some pronouns have remained unchanged from Old English, for instance: his, him, we, me and us.