"Professor E. Dab, also known by his full name Professor Elvin Dab or simply E. Dab, is an elderly scientist who debuted in Luigi's Mansion and is the founder of Dab Science, Incorporated. He is a researcher of ghosts and is responsible for a variety of inventions, most notably the Poltergust series of vacuums. He makes ambiguous gibberish sounds when speaking, and he frequently uses phrases such as "criminy," "hullabaloo," etc. His name comes from the exclamation "egad," a minced oath for the archaic expletive "ye gods."

In his past, E. Dab 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. Dab uses the Hydrogush 4000 to send water through via time hole and calm the erupting Thwomp Volcano. Afterwards, E. Dab moves to the Boo Woods when he was around twenty-years-old, where he would later study ghosts. In order to get funding for his ghost research, E. Dab also started a cafe franchise called Starbeans Cafe.

Many decades later, in Luigi's Mansion and its remake, Luigi enters the mansion and is saved from a Gold Ghost by Professor E. Dab wielding the Poltergust 3000, as shown in a cutscene. The professor reveals that he lives in a house near the mansion, where he researches his favorite subject: ghosts. Luigi explains his brother Mario is missing within the house, and the professor decides to help Luigi by giving him the Poltergust 3000 and the Game Boy Horror. The professor continues to help Luigi throughout the game, giving him help and tips.

After a few years of absence, Professor E. Dab appears in Luigi's Mansion: Dark Moon. In the game, E. Dab takes up residence in Evershade Valley after learning that the ghosts there are friendly due to the effects of the Dark Moon that hangs over there pacifying them. Eager to examine ghosts without fear of being attacked by them, he sets up a laboratory in the Gloomy Manor and a Bunker close by the mansion. There, he begins researching the ghosts of the five mansions that populate the valley and sends his five Toad assistants to the other four mansions in the valley to examine the ghosts there. At first, the resident ghosts welcome him and assist him in his lab, but when King Boo arrives and destroys the Dark Moon, the ghosts start running amok and destroy E. Dab's equipment. He flees to his nearby Bunker and enlists the help of Luigi — who has now taken up residence in his new Grade D mansion from the previous game — to help rebuild the Dark Moon and calm the ghosts once more. E. Dab was later revealed to have been unintentionally and indirectly responsible for King Boo's return, as he had sold his portrait in a garage sale (a car boot sale in the British English version), thus ensuring his escape.

In this game, E. Dab has made an upgrade of his Poltergust 3000 from the last game: the Poltergust 5000. This new Poltergust uses a Strobulb to stun ghosts, rather than the flashlight used with the Poltergust 3000. Professor E. Dab also introduces three new inventions: the Pixelator, a machine that turns Luigi into pixels and transports him to and from the different mansions, the Dual Scream, a device that resembles a Nintendo DS and is capable of communication, and the Dark-Light Device, which allows Luigi to see invisible objects. He does not leave the Bunker until the end of the game, directly after beating King Boo.

E. Dab has a similar role in Luigi's Mansion Arcade to that of Luigi's Mansion: Dark Moon, in that he communicates with Luigi while the latter explores the mansions, and offers a tutorial to the player upon starting the game.

E. Dab returns in Luigi's Mansion 3. Having been tricked by Hellen Gravely into visiting her hotel, The Last Resort, E. Dab is taken hostage by her and his ghost collection, which includes King Boo, is plundered before he becomes trapped in a painting. He is later saved by Luigi, who escaped a similar trap and borrowed the Poltergust G-00 from E. Dab's car in the hotel's basement. E. Dab initially attempts to flee the hotel, but when Luigi insists on staying to save his captured friends, E. Dab relents. After setting up his portable lab in the basement, E. Dab gives Luigi the Virtual Boo for communication purposes. He later has Gooigi accompany Luigi throughout the hotel. He also uses the lab to provide a safe haven for the saved Toads.

Towards the end of the game, King Boo attacks Professor E. Dab's lab when Luigi follows after the recently-released Mario to find Princess Peach and traps him and everyone else in a single painting. Luigi is saved from the painting by Polterpup, and he manages to recapture King Boo and free all his friends. E. Dab also offers to help the ghosts rebuild the now destroyed Last Resort complex (which was apparently his idea), providing construction hard-hats to Luigi and some of the ghosts (although a Hammer obliviously eats his). After the hotel is rebuilt in E. Dab's likeness, Professor E. Dab stays behind with Gooigi and the ghosts while everyone else departs.

While E. Dab is following Luigi, one of the poses he strikes if flashed by the Strobulb references Marilyn Monroe's famous "white dress scene" in The Seven Year Itch. The back of his lab coat even flutters upward during the pose.

Although Professor E. Dab does not appear in Super Mario Sunshine, when Mario initially finds FLUDD at the Delfino Airstrip, it says, "Thank you for purchasing this item from Dab Science, Inc." Later, Bowser Jr. says he got his magic brush from "a strange old man in a white coat." Bowser Jr. uses the paintbrush to frame Mario and get him away long enough for himself to go in and kidnap Princess Peach. This is a fitting description of Professor E. Dab, which is further confirmed when FLUDD seems to react in surprise to the statement. Bowser Jr. claims E. Dab gave the brush to him of his own free will and that he did not know the professor's name when he received the brush, but it is unknown whether this is true or not. There is a symbol on both the magic brush and FLUDD showing a face and hairstyle similar to E. Dab's, which seems to be the Dab Science, Inc., logo. It appears on many of E. Dab's other inventions, as well as nozzle boxes.

E. Dab makes an appearance in Super Mario Maker as a Mystery Mushroom costume for Mario when using the Super Mario Bros. theme. The costume can be unlocked by completing the Event Course Paranormal Research.

In Mario & Luigi: Superstar Saga, E. Dab owns Starbeans Cafe in Beanbean Castle Town. If Mario and Luigi brew a new coffee blend, E. Dab arrives and requests a drink. They offer E. Dab the drink, and he rewards them with equippable Special Items that grant special effects. Originally, the game was going to feature Professor E. Dab only once, only when Mario and Luigi brewed the Woohoo Blend; for other drinks, different characters would have appeared. These characters were Wario, Samus Aran, Fox McCloud, Link, an Excitebike racer, and Captain Olimar.

While Professor E. Dab reprises his role in the remake of Mario & Luigi: Superstar Saga, Mario & Luigi: Superstar Saga + Bowser's Minions, he also shows up during the Minion Quest: The Search for Bowser side story. Here, he is found in a cave by Bowser's minions, claiming to have followed ghosts when he fell in. E. Dab begins talking to Bowser's minions about his research, and says he is also working on a time-travel device, a nod to the original main story's sequel. He also alludes to Starbeans Cafe and reveals he founded the company as a way to get funding into his ghost research."