John Calvin was a theologian and pastor during the Protestant Reformation. Think of him as the French version of Martin Luther.
And many of his ideas are still widely regarded in Christianity today — a helpful tool for remembering his most basic ideas is the TULIP acronym.
Total Depravity: Human nature is corrupt and sinful as a result of the Fall.
Unconditional Election: God predestined some people to receive salvation.
Limited Atonement: Christ has saved those who hear and obey him, but not all will be saved.
Irresistible Grace: When God has chosen to save someone, we cannot refuse it.
Perseverance of the Saints: You cannot lose your salvation.