The Last Supper
All Christian liturgies of Holy Communion are modeled on the last supper
of Jesus with his disciples the day before his crucifiction. There are
descriptions of that last supper in all four of the canonical gospels
(Mathew 26:17-29, Mark 14.12-21; Luke 22.7-13; John 13.21-30). Only the
synoptic (Matthew, Mark, Luke) specificaly describe
the institution of the Sacrament of Holy Communion.
The authors of Matthew, Mark, and Luke all describe the way in which the Last Supper was organized and why. The Last Supper was a celebration of the Jewish Passover meal called the "Passover Seder." The "Passover Seder" is a Jewish ritual feast held on the first night of the Jewish holiday of Passover (the 15th day of Hebrew month of Nisan). Jesus instructed two of his disciples (Mark 14:13), probably Peter and John (Luke 22:8), to make the preparations for the meal.
Those in attendance at the meal were at least the twelve disciples we have come to call the Apostles. For a complete list, click the "Apostles" tab. There may have been others in attendance, as well, but they are not documented by the Gospel writers. Possibilities include Matthias (who was to become the replacement for Judas Iscariot after Judas' betrayal and death), Mary, the mother of Jesus, and Mary Magdelene, all of whom were almost always with Jesus throughout his ministry. At the very least, however, there were the twelve primary disciples.
That last supper of Jesus has been depicted by artists many times over the centuries. The most famous is probably that of Leonardo da Vinci, although there are many others. You can see some of these artistic renditions here: