This trade union was founded by Terrance Powderly in 1869 and became the first truly popular and successful unions in US history.

The answer is Knights of Labor or also known as K of L. But it was formally known as Noble and Holy Order of the Knights of Labor. It was the biggest and one of the most significant American labor unions of the 1880s. Its most significant leader was Terence V. Powderly. They began originally as a secret society organized after Free Masonry with the objective of supporting the organization of working individuals.