Who was the King of England before Queen Victoria and how long did he reign for?

Queen Victoria's predecessor was her uncle, King William IV who reigned from 26 June 1830 - 20 June 1837.

Neither he nor Queen Victoria were monarchs of England, during their reigns the official name of the country, from which the title of the monarch follows, was The United Kingdom of Great Britain and Ireland.

England is a part of, but not the same as, The United Kingdom.

See the related question below.