Little is known of Beni's past: a Hungarian con artist and soldier, he was a member of the French Foreign Legion during the 1920s, supposedly a friend to fellow Legionnaire Rick O'Connell. On the orders of an overambitious commander, they were part of a garrison sent out of Libya and into the Egyptian desert to search for the lost city of Hamunaptra; though they found the city, they were quickly attacked by the Medjai defenders. Before the army could even reach the Legion's front lines, Beni fled the scene for the safety of the ruins - casually abandoning Rick to die at the hands of the Medjai by sealing the door behind him.
After making his way back to civilization, Beni leaves the Legion altogether and sets himself as a fraudulent guide: as he eventually makes clear, his business thrives by charging exorbitant sums to lead travelers to Hamunaptra, only to abandon them in the middle of the desert before they could ask for their money back. However, he eventually ends up being hired by a party of American treasure-hunters who are smart enough to only pay half the agreed fee - the other half being paid upon their safe return to Cairo.
While accompanying the Americans on a ferry down the Nile, he bumps into Rick again; though Rick decides against killing him, he takes great delight in hurling Beni overboard. Unfortunately, this allows him to take the lion's share of horses and provisions when the Medjai attack the barge and force the adventuring parties overboard. Fortunately, Beni's party end up on the wrong side of the river, allowing Rick and the others a headstart to Hamunaptra.
Later, when the two parties finally arrive at the lost city, the American treasure-hunters are the first to uncover a find of real value: a sealed casket containing Anck-su-namun's canopic jars and the Book of the Dead. However, the curse inscribed on the casket spooks Beni, and he flees before the box can be opened - unwittingly saving his life in the process; when Evelyn reads from the book and accidentally resurrects Imhotep, Beni is one of the few members of the party not to be targeted by the mummy for assimilation. However, after abandoning Mr Burns in the tunnels under Hamunaptra, he is soon confronted by Imhotep (now sporting Burns' stolen eyeballs and tongue); in a panic, Beni begins reciting prayers in a number of different languages in the hope that one of them might be able to save his life. Recognizing Hebrew ("the language of the slaves") among one of the prayers, Imhotep spares Beni's life in exchange for his services as a translator, offering a handful of golden funerary treasure to sweeten the bargain.
From hereon, Beni serves as Imhotep's minion, not caring that it means the death of his supposed friends and the entire world being doomed if Imhotep wins. Over the course of the movie, he helps the mummy track down and kill the cursed Americans one by one, even mocking the horribly-mutilated Burns as he pleads for his life; for good measure, he also helps search for the Book of the Dead - though this once again brings him within punching distance of Rick O'Connell.
After helping to capture Evelyn and deliver her to Hamunaptra, Beni is left unsupervised while Imhotep begins the ritual to resurrect Anck-su-namun; recognizing an opportunity to profit further before fleeing, he gathers up as much of the city's treasure as possible and loads them into the saddle bags of his camels. However, his greed is ultimately his undoing: not satisfied by the small fortune already loaded, he returns to the treasure vaults for more - only to accidentally trigger an ancient booby trap in the process. Trapped in the collapsing tunnels under Hamunaptra, he is sealed inside the treasure vault as flesh-eating scarabs fill the room, presumably eating him alive.
Beni is a lying, cheating, cowardly crook. He has a habit of running from danger, betraying his "friends", or what he considers his friends, and even joining, what he considers to be, the winning side just to stay alive. Beni is also shown to be extremely greedy and rather stupid, as shown at the end of the movie. Beni tries to grab as much gold as he could before he tries to escape the collapsing tomb, but as a result, the tomb closed in on him, leaving him sealed, and eventually eaten by the Scarabs.
- Though not appeared in The Mummy: The Animated Series which based on the first two film that set on its own continuity, Beni was heavily referenced on Colin Weasler, whom regarded by fans as Beni's animated version.