Blitzen the Reindeer

In traditional festive legend, Santa Claus's reindeer pull a sleigh through the night sky to help Santa Claus deliver gifts to children on Christmas Eve. The commonly cited names of the reindeer are Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Donner, and Blitzen. They are based on those used in the 1823 poem "A Visit from St. Nicholas" (commonly called "The Night Before Christmas"), arguably the basis of the reindeers' popularity.

The enduring popularity of the Christmas song "Rudolph the Red-Nosed Reindeer" has led to Rudolph often joining the list.

In traditional lore, Santa Claus's sleigh is led by eight reindeer: Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Dunder (variously spelled Donder and Donner), and Blixem (variously spelled Blixen and Blitzen), with Rudolph being a 20th-century inclusion.

The names Dunder and Blixem derive from Dutch words for thunder and lightning, respectively.

The first reference to Santa's sleigh being pulled by a reindeer appears in Old Santeclaus with Much Delight, an illustrated children's poem published in New York in 1821. The names of the author and the illustrator are not known. The poem, with eight colored lithographic illustrations, was published by William B. Gilley as a small paperback book entitled The Children's Friend: A New-Year's Present, to the Little Ones from Five to Twelve.

The 1823 poem by Clement C. Moore "A Visit from St. Nicholas" (also known as "'Twas the Night Before Christmas") is largely credited for the contemporary Christmas lore that includes eight named reindeer.

The relevant segment of the poem reads:

When, what to my wondering eyes should appear,
but a miniature sleigh, and eight tiny rein-deer,
with a little old driver, so lively and quick,
I knew in a moment it must be St. Nick.

More rapid than eagles his coursers they came,
And he whistled, and shouted, and call'd them by name:
"Now, Dasher! Now, Dancer! Now, Prancer, and Vixen!
"On, Comet! On, Cupid! On, Dunder and Blixem!

"To the top of the porch! to the top of the wall!
"Now dash away! dash away! dash away all!"

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Wikipedia