Nigel Billingsley is a field guide within Jumanji.
Jumanji: Welcome to the JungleEdit
In the story of the game, Nigel was hired by Russel Van Pelt to guide him through Jumanji on a quest to find the Jaguar Shrine, resting place of the Jewel of Jumanji, claiming he wished to document the jewel in his writings. However, he was instead there to claim the jewel for himself, causing a curse to befall Jumanji and possessing him with a dark power, granting him control over the jungle creatures.
Nigel begged Van Pelt to put the jewel back, but he refused, so while the camp slept that night, Nigel stole the jewel and ran, sending a letter to Dr. Smolder Bravestone to come and help him return the jewel and lift the curse.
Upon completing the game. Nigel will arrive to shake the player's hand to send them home.
Because Nigel is an NPC, his ability to respond to the players actions is limited; possessing only a set pool of dialogue from which he cannot deviate. This is because his character exists primarily to provide exposition and set up details.
Similarly he cannot go beyond his role in the story, as while Nigel within the background, could have attempted to return the jewel himself before Van Pelt was ready to resist, doing so would invalidate the main mission for the player characters rendering the game pointless.