In America, this name received a boost of popularity in 2000 when a character bearing it began appearing on the television series The West Wing.
This was the name of several dukes of Brittany, and Breton settlers introduced it to England after the Norman Conquest. Famous modern bearers include Alan Shepard (1923-1998), the first American in space and the fifth man to walk on the moon, and Alan Turing (1912-1954), a British mathematician and computer scientist.
The Cornish form of this name, Jennifer, has become popular in the English-speaking world.
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.