The pater familias (sometimes written together paterfamilias) was the head of the Ancient Roman household. Very often it was the oldest man in the familiy. His family consisted of his wife, his children, his slaves, and other relatives. His duty was to represent the family to the outside, towards the state, but also towards the gods. If his sons married, their wives and children were also subject to the pater familias. He had supreme power, called patria potestas. This also meant that he was a judge in family matters. As such, he has the right to decide over life and death of the family members (called ius vitae necisque - the right [to decide] over life and death)
When the Pater famliias died, his children would become free from his power. His sons would usually rise to the position of pater familas of their famillies.
Only Roman citizens could become pater familias