Tristan -- known through medieval legend and Wagnerian opera -- has a slightly wistful, touching air. This, combined with the name's popular "an" ending, makes Tristan very appealing to parents seeking a more original alternative to Christian.
Tristan has been growing in popularity since the 1970s, moving in and out of the Top 100 since 1996, now at Number 87. One influence was the character Tristan Ludlow played by Brad Pitt in the 1994 movie The Legends of the Fall, based on a Jim Harrison novel.
Tristan is a dragon-slaying hero of Celtic legend, whose story was incorporated into Malory's Le Morte d'Arthur, in which Tristan is one of the Knights of the Round Table, consumed by his doomed love affair with Queen Isolde. Wagner set the story to music in his opera "Tristan und Isolde."
Tristan and its alternate form Tristram have been found in later lit as well. Tristram Shandy is a famous early comic novel by Laurence Sterne (in which the hero's father calls Tristram the worst name in the universe); Tristan is a major character in James Herriott's All Creatures Great and Small, and there is an eponymous novella by Thomas Mann.
Though Tristan was the male figure in the romantic legend and his name has become trendy for boys, it's used now for girls, too, much more often than the harder-sounding Isolde.