According to tradition, Santa's nine reindeer are named Dasher, Dancer, Donner, Blitzen, Comet, Cupid, Dancer, Vixen and the red-nosed reindeer, Rudolph. They were first brought together in Robert L. Mays' 1939 book "Rudolph the Red-Nosed Reindeer," published by Montgomery Ward as a Christmas advertising promotion.
The original eight non-red-nosed reindeer were first named in Henry Livingston, Jr.'s 1822 poem "A Visit from St. Nicholas." Livingston's original poem, however, named Donner and Blitzen "Dunder" and "Blixem," Dutch words translating to "thunder" and "lightning." In 1844, Clement Clark Moore, who is traditionally credited with writing the original poem, modified the two names to Donder and Blitzen. Mays' "Rudolph" changed Donder's name one last time, to Donner. At the same time, Mays invented Rudolph for his story. Mays' brother-in-law was a rising young songwriter named Johnny Marks. When Montgomery-Ward gave Mays the rights to "Rudolph," Mays in turn gave Marks the right to create a song based on the poem. This song, also named "Rudolph the Red-Nosed Reindeer," was picked up by Gene Autry in 1949, becoming an instant Christmas classic.
The names Donner and Blitzen are often thought to be based on German words. However, Livingston's entire poem was likely an Americanized version of the Dutch legend of Sinterclaas. It's probable that the modern versions were Germanized because German was a more familiar language at the time than Dutch.