Reverend Theo Kerr is the main human antagonist in The Lost World. He is played by Peter Falk. He was made entirely for the movie by creators Tony Mulholland and Adrian Hodges and he does not appear in the original Sir Arthur Conan Doyle novel.
When Professor Challenger and his expedition come to South America, they shelter at Reverend Kerr's house for the night. During their stay, they get into an argument about religion vs science. Professor Challenger is rude to his host by mocking The Bible, and mocking the priest's faith. His niece, Agnes, does not believe in religion but she respects his faith and lets him be. However, he attacks Challenger and the others by saying that evolution is Satan's work and the fossils found are of the creatures drowned in the Flood. Challenger mocks him by saying "...The ones who didn't make it into the Ark, I suppose."
When the group goes on their journey, their native guides see Voodoo ornaments in the jungle and abandon them. Reverend Kerr mysteriously joins them later, prompting Edward Malone to suspect Kerr may have been behind the natives' fright. However, nothing is proven and they reach the Plateau. However, Kerr betrays them all by chopping down their only bridge home and saying the dinosaurs were creatures of the Devil. Lord Roxton is on the bridge when Kerr is chopping it down, and almost falls to his death, but he is holding the rope which saves him.
Kerr nonchalantly looks at them stranded on the cliff and then makes his way down the cliffside.
Reverend Theo Kerr does not reappear until later in the film when he is attacked by the Ape-Men and survives an encounter from them, albeit gravely injured. He says they are monstrosities and how Satan sealed off the Plateau. He says no one will go home and attacks Professor Challenger, but Malone shoots him dead.