Around 1920, a 15-year-old Montana boy named Reindeer Coffman was in the news.
Reindeer’s baby brother had died while Reindeer was babysitting. At first, murder was suspected. Later, it was revealed that Reindeer had simply neglected the baby, who proceeded to accidentally strangle himself. (The baby’s shirt collar got caught on a protruding nail.)
One article about the case included a few lines about Reindeer’s name:
The boy’s unusual name caused [Humane Officer A. E. Decew] to make inquiries as to its genuineness. He found not only that Reindeer was called by his correct name but that there was a still more unusual name in the family. Reindeer has a brother named Rainbow.
Sure enough, both Rainbow and Reindeer (spelled “Rainder”) were listed together on the 1920 U.S. Census:
Their parents were William and Mina, and their siblings had the more common names Warren, Emery, Frances, Iona, Henry, Myrtie, Charles, and Allen.
Source: “Nail catches dress, baby is strangled, is brother’s tale.” Great Falls Daily Tribune 13 Mar. 1920: 13.