From Saint Luke's Acts of the Apostles:
Now in these days when the disciples were increasing in number, a complaint by the Hellenists arose against the Hebrews because their widows were being neglected in the daily distribution. And the twelve summoned the full number of the disciples and said, "It is not right that we should give up preaching the word of God to serve tables. Therefore, brothers, pick out from among you seven men of good repute, full of the Spirit and of wisdom, whom we will appoint to this duty. But we will devote ourselves to prayer and to the ministry of the word." And what they said pleased the whole gathering, and they chose Stephen, a man full of faith and of the Holy Spirit, and Philip, and Prochorus, and Nicanor, and Timon, and Parmenas, and Nicolaus, a proselyte of Antioch. Acts 6:1-5 (ESV)
The title of Deacon will have different connotations for individuals that will be driven by their individual church traditions. While Deacons may be found in a number of Christian churches, their roles and functions will vary to a wide degree. The Southern Baptist will be a man and lay member who ostensibly serves much like a Church council member of Vestry member. The Roman, Orthodox, or Anglican Deacon will be members of the Clergy. The former will be male and the latter may be male or female. Going forward, I'll be discussing the topic through an Anglican lens.
The Deacon is the oldest existing office of ordained ministry within the historic orthodox church. While one might rightly point out that Deacons were ordained by the Apostles, the Apostolic office ceased with the passage of Saint John. (Some today might claim the title of "Apostle", but they're pretenders to that position). It was an office created to come alongside the Twelve in order that they might be able to give greater focus on the communication of the Gospel message. The twelve understood that their ministry wasn't "too important" for caring for human needs, but that these human needs were of critical importance and required additional hearts and hands to come along the Apostolic, to create a greater holistic ministry as both spiritual and physical needs were being ministered to.
One of these initial seven, Stephen, would become the Church's first Martyr, dying under a hail of stones. There would be others and there is sound evidence that this wasn't solely a masculine office. One female Deacon was Phoebe who was associated with the Church in Cenchreae, a village near the Greek city of Corinth.
Today, you'll find Deacons throughout the Church, while their ministry will vary.