Karl E. Linderfelt was a soldier, mine worker, soldier of fortune, and officer in the Colorado National Guard. He was reported to have been responsible for an attack upon, and the ultimate death of, strike leader Louis Tikas during the Ludlow Massacre. He was the son of librarian Klas August Linderfelt.

Klas August Linderfelt was an American librarian. A native of Sweden, he emigrated to Milwaukee, Wisconsin and became a teacher and a librarian. As the first librarian of the Milwaukee Public Library, he became a significant figure in the city and in the library profession, becoming the seventh President of the American Library Association. He left both the city and the profession permanently following his arrest for embezzlement.