Duke is the apparent leader of the Dino Riders and is what appears to be a dark green Rex wearing a leather-jacket and brown helmet. Duke is also abnormally short. Rockman is Duke's right-hand man and is exceptionally huge and menacing-looking. Lulu is the final member of the gang and the only girl in it, she appears to be some kind of lizard.
The Dino Riders are first seen when Yoshi is running-away from home; the Dino Riders drive-up to Yoshi on their motorcycles and begin to question him. After learning that Yoshi knows Mario and Luigi, Duke allows Yoshi to join the Dino Riders; secretly though, the Dino Riders simply wanted to use Yoshi to get to the Mario Bros., who they planned to capture and sell to Bowser.
Manipulating Yoshi, the Dino Riders had the oblivious reptile commit several bad-deeds such as graffiti and stink bombing a house before granting him "full membership" into the gang. Duke then had Yoshi tell Mario and Luigi to meet with the Dino Riders at the Tar Pit Milk Bar. Venturing to the bar, Mario and Luigi were captured by the Dino Riders, who set-off to Bowser's Neon Castle to turn the Bros. in.
While on their way to Neon Castle, the Dino Riders were ambushed by Yoshi and Princess Toadstool, who rescued Mario and Luigi from the Dino Riders. Stealing Lulu's motorcycle, Mario, Luigi, Yoshi and Princess Toadstool took-off, with the Dino Riders hot on their trail.
The Dino Riders were eventually defeated when, during a high-speed chase, Rockman was blasted into and deep-fried in a lava pit, while Duke and Lulu crashed into a wall. Duke, Lulu and Rockman were last seen staring into the Warp Tube that Mario, Luigi, Yoshi and Princess Toadstool had escaped down.