After the Protestant Reformation it was occasionally used as a given name in the English-speaking world, and it became somewhat common in America due to the fame of the revolutionary Ethan Allen (1738-1789). It only became popular towards the end of the 20th century. It is the name of the main character in Edith Wharton's novel Ethan Frome (1911), about a man in love with his wife's cousin.
This name was initially more common among Eastern Christians in the Byzantine Empire, but it flourished in Western Europe after the First Crusade. In England it became extremely popular, typically being the most common male name from the 13th to the 20th century (but sometimes outpaced by William). During the later Middle Ages it was given to approximately a fifth of all English boys. In the United States it was the most common name for boys until 1923.
The name (in various spellings) has been borne by 21 popes and eight Byzantine emperors, as well as rulers of England, France, Sweden, Denmark, Poland, Portugal, Bulgaria, Russia and Hungary. It was also borne by the poet John Milton (1608-1674), philosopher John Locke (1632-1704), American founding father and president John Adams (1735-1826), and poet John Keats (1795-1821). Famous bearers of the 20th century include author John Steinbeck (1902-1968), assassinated American president John F. Kennedy (1917-1963), and musician John Lennon (1940-1980).
The forms Ian (Scottish), Sean (Irish) and Evan (Welsh) have also been frequently used in the English-speaking world, as has the medieval diminutive Jack.
As a given name it was mostly masculine in America until around 2009. It was already rising in popularity for girls when singer Mariah Carey gave it to her daughter born 2011 (though this probably helped accelerate it).
As a given name for boys, it gained some popularity in the mid-1990s after the debut of the American television series Nash Bridges. It got more exposure beginning 2005 when a character by this name started appearing on the soap opera One Life to Live.
Very rare as an American given name before 1980, it increased in popularity in the 1980s and 90s. It got a boost in 2004 after the debut of the television series Lost, which featured a character by this name.