|Country||22x20px United States|
|Trainer||Jack "Swede" Lindell|
His trainer was Jack "Swede" Lindell, who found him in a boy's school in Flagstaff, Arizona. He found that Rex had the unusual behaviour of trying to bite a whip when it was cracked. Lindell encouraged this and would often stand behind the camera to get a dramatic shot on film. Lindell never left Rex alone on set unless he was locked in his own trailer.
During filming of The Law of the Wild Rex made a commotion on set. When he charged the camera (with Lindell behind it) as intended he did not stop when Lindell gave the signal to do so (by holding his whip in both hands). He reared, knocking over several reflectors and causing the cast and crew to scatter for cover. Rex chased one actor, Ernie Adams, who attempted to hide under a car. Rex dropped to his knees and attempted to bite Adams with his head thrust sideways underneath the car. Lindell managed to call Rex off by simply cracking the whip, after which the horse calmly walked over to him. When William Witney, working as an assistant director on the serial, made Stranger at My Door (1956) he described the event to trainer Glen Randall and the scene was recreated for that movie.
- Stormy Actor (1935)
- The Law of the Wild (1934)
- The King of the Wild Horses (1934)
- The Harvest of Hate (1929)
- Hoofbeats of Vengeance (1929)
- Wild Beauty (1927)
- No Man's Land (1927)
- No Man's Law (1927)
- The Devil Horse (1926)
- Black Cyclone (1925)
Another horse appeared under the name of Rex the Wonder Horse in Robinson Crusoe of Clipper Island (1936) but it was not the same animal.
- PDF by Susan Graf