According to the Coptic church, it was founded by the eunuch which Philip led to Jesus in Acts 8:26-39. They claim to be the oldest segment of Christianity continuous to today.
I can see the Ethiopian Coptic Church claiming to trace their history back to the eunuch baptized by the deacon Philip, but the Egyptians? St. Mark the Evangelist is said to have founded the church in Alexandria (which is the reason the bishop of Alexandria later ranked as one of the patriarchs), and St. Mark would certainly be considered far more important and prestigious than an unnamed eunuch. Moreover, eunuchs were widely despised and looked down on. I think the Egyptian Coptic Church must claim St. Mark.