Gérard is a disgraced archaeologist and former associate of Professor Bresson, dismissed from academia for unethical methods and an obsession with uncovering the secrets of the Bresson Diary. For decades, he sought the diary, believing it held the key to an immense power source called the Eclipse.

To achieve his goal, Gérard manipulated Laetitia, Professor Bresson's granddaughter. He posed as her friend and mentor, Jean-Paul, exploiting her desire to restore her grandfather's reputation to guide her towards recovering the diary. His true motivations were personal power and historical vindication. He orchestrated events to pit Laetitia against Arsène Lupin III and his crew, using her to unlock the diary's complex mechanisms. Once the diary was fully activated, he discarded his Jean-Paul persona, revealing his true identity and intentions to Laetitia.

Securing the diary, Gérard traveled to the hidden Third Reich facility beneath Paris where the Eclipse device was constructed. He activated the device, driven by a desire to wield its destructive power, demonstrating a ruthless willingness to sacrifice others, including Laetitia. In the final confrontation within the Eclipse facility, Gérard was defeated by Lupin and his allies. He perished when the collapsing facility flooded, a result of the battle and the destructive instability of the Eclipse device. His obsession led directly to his downfall.