Oh Henry! Commercial 1999

There are multiple versions of the Oh Henry! bar origin story. The manufacturer Nestlé says that the bar was introduced by George Williamson and his Williamson Candy Company of Chicago in 1920 in the United States. The most popular alternate story is that Thomas Henry, manager of the Peerless Candy Co. in Arkansas City, Kansas, invented a bar he called the "Tom Henry Bar" in the late 1910s and sold the recipe to George Williamson in 1920. There is no credible documentation of this story, however.

There are other alternate accounts of the origin of the name of the bar. The story supported by Nestlé is that there was a boy named Henry who frequented George Williamson's second candy shop. He became a favorite of the young girls who worked there, who would say "Oh Henry" when speaking to or about him, and Williamson used this phrase to name his new confection. The other (undocumented) story is that the name was changed from the Tom Henry Bar to Oh Henry! when it was purchased by Williamson. Popular myths are that it was named after O. Henry or Henry Aaron.

The Williamson Company was sold to Warner-Lambert in 1965, which soon sold Oh Henry! to Terson, Inc. Nestlé acquired the United States rights to the brand from Terson in 1984. In 2018, Nestlé sold the rights to its U.S. confectionery products to Ferrara Candy Company, a subsidiary of Ferrero SpA.