This could probably be rerouted to our Short Answers to Simple Questions thread, but the answer is fairly straightforward. The first king of "the English" as he was styled was Alfred the Great, of the house of Wessex, whose descendants ruled England until the time of Queen Anne; Alfred's grandson Æthelstan (son of Edward the Elder and his first wife Ecgwynn) is generally considered the first king of "England."

After the Acts of Union in 1707, Queen Anne was the ruling monarch of the new country called Great Britain. Anne having been pregnant at least 17 times but with no living children, when she died the crown passed to her second cousin, George of Hanover, who became George I of Great Britain as the closest related non-Catholic heir to the throne (he was the great-grandson of James VI and I, who ruled over England and Scotland in a personal union).