Professor Elvin Gadd

Luigi: Good friend
Googi:Invention
King Boo:Enemy

In his past, E. Gadd lived on the foothills of the Thwomp Volcano, as depicted in Mario & Luigi: Partners in Time. The Mario Bros. go back in time and end up saving his lab from burning down when fire blocks erupted from the Thwomp Volcano. He then helps the Mario Bros. by inspiring his older present self to create the Hydrogush 4000; As the Mario Bros. are in the present, he starts to get the idea for the device, which transfers to his future self. The present-day Professor E. Gadd uses the Hydrogush 4000 to send water through via Time Hole and calm the erupting Thwomp Volcano. Afterwards, the twenty-year-old E. Gadd moves to Boo Woods, where he would later study ghosts.

Poltergust 3000 (LM1): A modified vacuum cleaner used to suck up ghosts and shoot elements.
Ghost Portrificationizer (LM1): A machine that converts captured ghosts into portraits.
Game Boy Horror (LM1): A handheld device used by Luigi for maps, radar, and communication with E. Gadd.
Poltergust 5000 (Dark Moon): An upgraded vacuum featuring the Strobulb for stunning ghosts.
Dark-Light Device (Dark Moon): An attachment to reveal invisible objects and ghosts.
Pixelator (Dark Moon): A device that converts Luigi into pixels for fast travel.
Dual Scream (Dark Moon): A Nintendo DS-shaped communication device.
E-Gates (Dark Moon): Electronic portals used for transportation.
Poltergust G-00 (LM3): The model in Luigi's Mansion 3 equipped with a plunger launcher.
Gooigi (LM3): A slimy, ectoplasmic clone of Luigi created to navigate hazards.
Virtual Boo (LM3): A headset device, reminiscent of the Virtual Boy, used for map and communication.
Other Notable Inventions
FLUDD (Super Mario Sunshine): Flash Liquidizer Ultra Dousing Device.
Magic Paintbrush (Super Mario Sunshine): Used by Bowser Jr..
Robo Mario (Mario Kart DS): Robotic replica.

E. Gadd is a short, elderly man with light skin. He has a small, thin piece of white hair and has a round head, with light blue, swirly glasses. As shown in certain angles of Luigi's Mansion 3, he has small, black eyes. He wears a dark red undershirt with a white, buttoned lab coat, and wears thin, black leggings and pointy, brown shoes.

Eccentric & Brilliant: He speaks in a unique, jumbled, or gibberish-like manner and is obsessed with studying ghosts.
Supportive Mentor: Despite his quirks, he acts as a father figure to Luigi, encouraging him to overcome his fears, as seen in Luigi's Mansion: Dark Moon.
Sarcastic Humor: E. Gadd can be playful, often teasing Luigi, such as when he jokingly trapped him in a cage while introducing Gooigi in Luigi's Mansion 3.
Dedicated Researcher: He is highly determined to analyze the paranormal, often prioritizing his investigation, which can make him appear slightly indifferent to the immediate, dangerous situations Luigi faces.