The names of Santa’s eight (or nine) reindeer have been immortalized in song: Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Donner, and Blitzen. However, in the original version of ‘Twas the Night Before Christmas, which was titled A Visit from St. Nicholas, the last two reindeer were named Dunder and Blixem.
The poem was published anonymously in a newspaper in 1823. The author, about which there is some debate, took bits and pieces from different mythologies about St. Nicholas and Santa Claus and added a sleigh with reindeer. Dunder and Blixem were Dutch words for thunder and lightning.
Because the authorship was anonymous, the poem was reprinted in various places. A few years after the first printing, someone changed Blixem to Blixen, conceivably to rhyme with Vixen. From there it was changed to Blitzen to match the German spelling of lightning.
There is less certainty about the change from Dunder to Donder and then to Donner. Different spellings pop up at different times and places. One thing is for sure, it was put firmly in place as Donner when Rudolph was penned in a song in 1939.
As a side note, all other six reindeer originally listed in the 1823 poem have stayed intact.
Examples
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! [Anonymous]Donner and Blitzen, two prominent reindeer who may or may not have taken part in the alleged bullying, were said to be cooperating with the investigation and providing details about specific instances of bullying. The victim’s identity has not been released. [Dans Papers]