Sidhu was Roland Tembo's friend from East India and lifelong hunting companion. Ajay is the one who convinced Roland to let himself be hired by Peter Ludlow, and tagged along on the expedition as well.
The Lost World: Jurassic Park
Sidhu and Tembo arrived to Isla Sorna, accompanied by the InGen hunters, and their new boss Ludlow, and soon rounded up some dinosaurs.
At nightfall, Sidhu and Tembo sneaked to the t-rexes' nest and took their infant in order to lure the buck coming to them. However, Tembo's plan to lure the buck was put on hold after Nick Van Owen and Sarah Harding infiltrated the camp, released the dinosaurs from their cages and took the infant away. The infiltration caused a major havoc at the camp, as well as leading the t-rex couple to Nick and Sarah, which cost Eddie Carr's life and put the others in grave danger when the furious parents pushed the trailer from the cliff. Tembo and Sidhu saved Sarah, Nick, and Ian by pulling them up and took them in to the larger group.
When the T-Rexes attacked the group, Ajay tried to stay with Roland, but two other hunters pulled him away. After outrunning the Doe, the group ran into the long grass. Ajay knew long grass is where Raptors lurk, but the other hunters were too panicked to listen to him. He followed, trying to stop them. Sadly, he only got himself killed when the pack of Raptors attacked the group.
Behind the Scenes
One of The Lost World's deleted scenes featured the main characters (including Ajay) hang-gliding to get away from the Velociraptors. The group makes out of the tall grass and over a cliff to safety, only to be ambushed by Pteranodons. Ajay (or another balding bespectacled character) was supposed to be ripped apart by the winged predators, a scene so gruesome that Sarah had to look away.
Another deleted scene shows Ajay meeting Roland in a bar and convincing him to join Peter Ludlow's team on Isla Sorna.
Roland made Dieter his second in command despite seeming to respect Ajay more. This is most likely for keeping his enemies closer, but possibly also because Ajay did not want the position Roland, even though that Ajay would make a better right hand man for their independent hunting trips on the island.
He's one of the only three antagonists in the franchise (along with Roland Tembo and Sammy Gutierrez) who is not a villain, even considered as more heroic than many protagonists.