St. Pachomius lived in the Egyptian Thebaid, and is to cenobitic monasticism what St. Anthony the Great is to the eremitic (solitary) way, and what St. Nilus of Sora is to skete life in Russia. He is commemorated on May 15.
From his Life at OCA.org:
Saint Pachomius the Great was both a model of desert dwelling, and with Saints Anthony the Great (January 17), Macarius the Great (January 19), and Euthymius the Great (January 20), a founder of the cenobitic monastic life in Egypt.
Saint Pachomius was born in the third century in the Thebaid (Upper Egypt). His parents were pagans who gave him an excellent secular education. From his youth he had a good character, and he was prudent and sensible.
When Pachomius reached the age of twenty, he was called up to serve in the army of the emperor Constantine (apparently, in the year 315). They put the new conscripts in a city prison guarded by soldiers. The local Christians fed the soldiers and took care of them.
When the young man learned that these people acted this way because of their love for God, fulfilling His commandment to love their neighbor, this made a deep impression upon his pure soul. Pachomius vowed to become a Christian. Pachomius returned from the army after the victory, received holy Baptism, moved to the lonely settlement of Shenesit, and began to lead a strict ascetic life. Realizing the need for spiritual guidance, he turned to the desert-dweller Palamon. He was accepted by the Elder, and he began to follow the example of his instructor in monastic struggles.
Once, after ten years of asceticism, Saint Pachomius made his way through the desert, and halted at the ruins of the former village of Tabennisi. Here he heard a Voice ordering him to start a monastery at this place. Pachomius told the Elder Palamon of this, and they both regarded the words as a command from God.