St. Anthony the Great is credited with being the first monk in that he did not just live an ascetic life, but also he removed himself from civilization and went into the desert. The eremitical (hermit) life appealed to many in the years to follow, but not everyone had the self-discipline to lead that kind of life. This is where Pachomius was needed.
St. Pachomius (c.292-348) was born a pagan. Drafted into military service by the Roman army, he noticed how Christians brought food to the conscripts. When he left the army a few years later, he investigated Christianity and converted in 314. After seven years as a hermit, he traveled to where St. Anthony was living, modeling his life after Anthony's solitary example. Then, however, a vision told him to create a community where others could join him.
Hermits had clustered together in the same area before, but Pachomius created an organized structure for monks who actually lived and worked together, holding their possessions in common and following a similar schedule. This style of monastic tradition is called cenobitic, a Latin word from the Greek words for "common" [κοινός] and "life" [βίος].
He created the first community shortly after this vision; the first person to join him was his brother John. Many more were to follow. Pachomius built nine monasteries, but the trend caught on: by the time of his death there were an estimated 3000 communities in Egypt. Pachomius was referred to as "Abba," [father], from which the terms "abbot" and "abbey" come. He also wrote the Rule of Pachomius, creating guidelines for communities. It is written in the Coptic (Egyptian) language.
Pachomius never was ordained as a priest. St. Athanasius visited him and wanted to ordain him in 333—Pachomius, like Athanasius, had proven to be a vocal opponent of Arianism—but Pachomius did not want ordination. He died on 9 May 348, presumably from plague.