Kadee
Kadee Quality Products Co. is a model railroad manufacturer. They are best known for their couplers, but also produce rolling stock and accessories. The coupler line covers HO and larger scales, but not N scale.
Kadee Quality Products was established in 1940 by identical twin brothers Keith and Dale Edwards. They named their company using their own initials, K and D. They were both toolmakers and capable engineers. Their claim to fame and financial success came when they developed and patented their HO knuckle coupler which became the de facto standard in the hobby.