The term 'Caroline' refers to the reign of which king?

The Caroline or Carolean era refers to the era in English and Scottish history during the Stuart period (1603–1714) that coincided with the reign of Charles I (1625–1642), Carolus being Latin for Charles. The Caroline era followed the Jacobean era, the reign of Charles's father James I (1603–1625); it was followed by the English Civil War (1642–1651) and the English Interregnum (1651–1660).

The Caroline era was dominated by the growing religious, political, and social conflict between the King and his supporters, termed the Royalist party, and the Puritan opposition that evolved in response to particular aspects of Charles' rule. In contrast, however, to the bloody conflict of the Thirty Years' War then raging in continental Europe, the Caroline period in Britain was one of an uneasy peace, growing darker as the civil conflict between King and Puritans worsened toward the latter part of Charles' reign.