When the soldier was decapitated like Massad before him, Donovan commanded Helmut to bring forward another "volunteer". While Helmut and a colleague carried out the order, Indiana Jones and his group were captured, and Helmut was directed to stand down, for Jones would be taking the volunteer's place instead.
When Elsa Schneider crossed the threshold with the Grail, causing a cataclysm that threatened to destroy the temple, Helmut and the other Nazi soldiers ran, leaping over the crack in the floor that formed. They barely made it and thereafter ran out.
Behind the scenes
Helmut was played by an uncredited performer in Indiana Jones and the Last Crusade.
According to his shoulder insignia, Helmut is a captain. However, because the Nazis in Hatay are wearing Heer (Army) uniforms, but taking orders from an SS officer, it's unclear whether Helmut would be a Hauptmann (Wehrmacht) or a Haupsturmführer (Schutzstaffel).
In the Last Crusade novelization, Helmut and his fellow soldiers receive a similar fate to that of Elsa Schneider, falling through the chasm that opens up in the Temple of the Sun's floor during its collapse.
In Indiana Jones and the Last Crusade: The Graphic Adventure, the player, as Indiana Jones, can encounter a soldier in Castle Brunwald named Helmut. It is unclear if this is intended to be the same character from the film as he is absent from the game's adaptation of the temple scenes.