Colonel Nsogbu is the leader of the soldiers from the "People's Army" whom Eric and his assistant Nigel have hired to help them capture a live specimen of the Mokele-mbembe, aka a living brontosaurus.
The Colonel gets off to a bad start with Eric right off the bat by first letting his rowdy, trigger-happy men throw a wild party on the ship taking them upriver, during which they bully and humiliate Nigel. Then, after they reach their destination and Nigel tranquilizes the female dinosaur, the male suddenly appears and tries to come to his mate's rescue.
Despite Eric's cry of, "Colonel, don't shoot!" Nsogbu orders his men to waste the animal with gunfire. When the beast is dead, an incensed Eric demands to know why he did that, whereupon Nsogbu explains, more or less, that with the male dead the female is twice as valuable alive.
From here on out Nsogbu does everything he can to antagonize and undermine Eric at every turn, especially where the captive dinosaur is concerned - namely that in order to keep the beast quiet, the Colonel continuously shoots her full of tranquilizers, with no regard for its long-term effects.
This disturbs Nigel greatly, and he comes to Eric with his worries. "I told him no more tranquilizers!" Eric hisses angrily. Assuring his assistant that he'll handle it, he grabs one of the tranquilizer darts and goes into Nsogbu's tent. He explains that he wishes to give the brontosaurus some medicine but that the gun he and Nigel have isn't the right size for the dart; he politely requests the use of the more specialized tranquilizer gun that Nsogbu keeps in his possession.
Apparently, he didn't get the memo about the guy Eric stabbed to death at the beginning of the movie, because, as Eric loads the dart into the gun, Nsogbu only halfheartedly inquires what it is. Eric simply replies that it's "some of our very best stuff," and then proceeds to let the Colonel have it, shooting him in the stomach with the dart.
Said projectile contains enough tranquilizer to knock out a multi-ton reptile, so you can imagine that it does quite a lot worse to an ordinary human. And, indeed, as Eric grabs the Colonel and covers his mouth to stifle his cries, it isn't long before Nsogbu is dead from a severe case of drug overdose to rival Funboy's.