Critics in the legal community dispute whether the "Super Hero" marks meet the legal standard for trademark protection in the United States: distinctive designation of a single source of a product or service. Controversy exists over each element of that standard: whether "Super Hero" is distinctive rather than generic, whether "Super Hero" designates a source of products or services, and whether DC and Marvel jointly represent a single source. Some critics further characterize the marks as a misuse of trademark law to chill competition. To date, aside from a failed trademark removal action brought in 2016 against DC Comics' and Marvel Comics' United Kingdom registration, no dispute involving the trademark "Super Hero" has ever been to trial or hearing.
The practice may have originated in a Celtic festival, held on 31 October–1 November, to mark the beginning of winter. It was called Samhain in Ireland, Scotland and the Isle of Man, and Calan Gaeaf in Wales, Cornwall and Brittany. The festival is believed to have pre-Christian roots. After the Christianization of Ireland in the 5th century, some of these customs may have been retained in the Christian observance of All Hallows' Eve in that region—which continued to be called Samhain/Calan Gaeaf—blending the traditions of their ancestors with Christian ones. It was seen as a liminal time, when the spirits or fairies (the Aos Sí), and the souls of the dead, could more easily come into our world. It was believed that the Aos Sí needed to be propitiated to ensure that the people and their livestock survived the winter.