Final answer:
King Charles I was the first English king executed by his own people, after tensions with Parliament led to the English Civil War and his eventual downfall.
Step-by-step explanation:
King Charles I was the first English king to be put to death by his own people. He ascended the English throne in 1625 and faced constant struggles with Parliament over his belief in the divine right of kings and matters of taxation and religious policy. During his reign, tensions escalated between the monarchy and Parliament, leading to the outbreak of the English Civil War.
His marriage to a French Catholic princess and attempts to rule without Parliament culminated in his execution in 1649, after which England experienced a period as a republic under Oliver Cromwell. The monarchy was restored in 1660 with the coronation of Charles I's son, Charles II, after the interregnum and Oliver Cromwell's death.