August Belmont Jr. founded the Interborough Rapid Transit subway line in NYC which became the IRT line and built the horse racing track which bears his name. As you’d pretty much expect, he had his own custom-built subway car that he used to travel to and from the track. When he died in 1924 it went out of use and has been moved around and stored in multiple places. In 2001 the NY Times reported that it still existed and was being kept at a trolley museum in Connecticut. Recently, Untapped Cities confirmed it was still there and was able to photograph the interior.