Proteus manifested in Midtown Manhattan in the 13th Floor of the Erie.  It served as a nexus of spectral activity, causing a lot of ghosts to appear, much like the coming of Gozer.    After capturing over 40 of the ghosts, the Ghostbusters were on their way to bust a Class 9 Free Roaming Vapor at the Gracie Mansion when Proteus attacked them while possessing the Atlas statue of the Rockefeller Plaza. He captured the Ghostbusters and made them his prisoners.
Janine had donned a uniform and brought some equipment with her to save the Ghostbusters. After learning that Proteus's lair was in the 13th floor of the Erie, she went there and saved her friends. She stopped the elevator between the 12th and 14th floor and found the hidden 13th floor. While Slimer distracted Proteus, Janine shot the mirrors that were holding the Ghostbusters in Limbo. This caused the nexus to overload and Proteus was clearly affected. The 13th floor of the building then exploding in much the manner that 55 Central Park West did when the Ghostbusters crossed their Proton Streams into the Temple of Gozer. The level of paranormal activity returned to normal after the explosion.
During the incident, Peter attempted to bill a civilian named Claudia after the Ghostbusters trapped Natasha, a ghost that happened to know her and wanted payback. He waived the usual call fee but Egon interjected and stated they weren't charging her anything since it was an exigent manifestation. Peter was not happy. More so when Claudia called out she would repay them as they drove away. They headed to Gracie Mansion and passed Rockefeller when the Proteus-possessed Atlas statue attacked them. Just as Proteus blasted them, Claudia cast a ward of protection. The Ghostbusters were accidentally teleported to a parallel dimension instead of Proteus' chosen nexus. Proteus realized what happened and teleported to Claudia's home. He paralyzed Claudia and her cat Hollis and figured out she was a witch. He demanded to know what happened. After vowing to get the Ghostbusters back, Proteus turned her into a blue bird as punishment and left her alone with Hollis.
Proteus returned to the Eerie and had the Dark Entity search for the Ghostbusters. The entity failed and Proteus summoned Ananke to aid him. Ananke tried to dissuade him by stating the Ghostbusters were mortals and beneath him but Proteus stated their were captors. Ananke realized Proteus was taking the initiative and tried to capture them before they captured him.  Proteus did not like her mockery and declared he truly wanted to restore the natural order of the world.  He didn't believe mortals should have power over gods and demons. Ananke didn't buy his admission of a noble purpose and implied it was their fate to be captors. She tried to warn him by revealing their fates were now linked with his. Proteus simply demanded to know where they were. Ananke remarked how remarkably short sighted he was acting and only told Proteus that the Ghostbusters were in New York. He was not pleased. Ananke then hinted at the existence of parallel dimensions and left.
Proteus began teleporting to various dimensions in search of the specific version of the Ghostbusters he ambushed. He eventually admitted his search was in vain. Upon teleporting to a version of the Bronx Zoo, Proteus was shot at by the Extreme Ghostbusters. He pulled Garrett Miller's proton stream and examined him up close. Proteus knew he hadn't found his quarry. He teleported back to the Erie to formulate a new plan. Proteus settled on creating a Cerberus Manifestation to blindly hunt for him. He instructed the manifestation to alert him the instant it found the Ghostbusters he wanted. After some time had passed, the Cerberus Manifestation succeeded in tracking down the Ghostbusters that Proteus desired. While Kylie Griffin shared her observations about its interest in the alternate team of Ghostbusters, Proteus arrived inside the Firehouse and stood atop the Ecto-1. Ray Stantz concluded it was time to send them back to their home dimension. Proteus made his presence known and agreed it was far past time they were back to where they belonged.
Proteus opened fire on the two teams of Ghostbusters. As they scrambled up to the second floor, Proteus took a moment to gloat. Janine Melnitz threw her paperweight at Proteus' head. He zapped her and Kylie Griffin, teleporting them to Tokyo. He punched through the second floor and shifted into a serpent form to avoid the Ghostbusters' attack. They made a run for the first floor. The Ghostbusters searched around and were almost stomped from above by Proteus. The two Egons armed their Proton Grenades and threw them. Proteus was amused at first but was stunned by the detonation. All eight Ghostbusters opened fire and wrangled Proteus. Since he was captured, Proteus was forced to conform to the restrictions of his gift of prophecy and reveal eight futures all at once. He showed images of the Louvre Museum, Poveglia, a woman, Sandman, The Deadly Three, Samhain, Grundel, and Tolay. Visibly weakened, Proteus considered taking both teams but decided against it on the grounds he wasn't greedy. He zapped the Ghostbusters he was after and teleported back to the Erie.
Janine and Slimer located the Erie and found the Ghostbusters trapped in Limbo. As they warned her, Proteus appeared and cycled through several forms. She fired at him to no avail but Slimer provided a distraction. Janine turned to the Ghostbusters and prepared to open fire on their prison. Ananke stopped time and paid her respects to Proteus before his defeat. He didn't believe her and declared he had won. Ananke pointed out he was weakened by a wearying trip to another dimension, assaulted by weapons he had no true defense against, and the stretching of his essence to show eight futures at once. She bid him farewell, restored time, and teleported away. Proteus powered his fingertip but Janine blasted the Limbo. The Ghostbusters, Janine, and Slimer vacated the Erie as Proteus' beam destroyed the building. The level of paranormal activity returned to "normal" and Claudia was restored to her normal self.
Proteus first appears at Rockefeller Center, possessing the iconic Art Deco statue of the mythological Greek Titan, Atlas. When Janine rescues the Ghostbusters, he assumes a variety of forms (a snake, a wolf, an unidentified 4 eyed creature, and an insect) and finally reveals his true form, that of a handsome, muscular blonde man in a Greek toga. Janine even complemented him, saying for a demon he wasn't bad looking.
A god of Greek Mythology, Proteus' most notable power is shape-shifting. He also has the ability to cast his enemies into limbo, a realm inside the mirrors of his lair, using bolts of lightning hurled from his fingertips. Proteus also has the ability to possess inanimate objects, such as the Atlas statue; and by doing so, he charged the statue with so much ectonic force, he could resist the Proton Streams. 
Proteus also showed the power of teleportation, paralyze victims in a spherical construct, transmogrify others, travel to other dimensions and time periods, and show glimpses of the future.
Proteus was confirmed to be a primal god like Gozer. If the animated version of Gozer's classification were revealed, it is likely Proteus would be of the same class.
- On page 11 of Ghostbusters Volume 2 Issue #1, Proteus' business Proteus Unlimited is referenced on Walter Peck's file.
- On page 7 of Ghostbusters Volume 2 Issue #13, Proteus Unlimited has a non-canon reference on the glass
- On page five of Ghostbusters Volume 2 Issue #19, Proteus makes a non-canon cameo as one of the forms of Gozer.
- On page five of Ghostbusters Volume 2 Issue #19, Proteus' snake form makes a non-canon cameo as one of the forms of Tiamat.
- In Get Real Issue #1, page 15, Ananke calls Proteus by his nickname from Greek mythology, "The Old Man of the Sea"  
- In Get Real Issue #1, page 16, Ananke alludes to a story in Greek myth where Proteus was captured by Heracles and forced to surrender the location of Garden of Hespericles. In myth, Proteus would only answer questions if he was captured. 
- In Get Real Issue #1, page 17, Ananke refers to Proteus' gift of prophecy in Greek mythology. 
- In Ghostbusters Get Real Issue #3, page 11, Ray notes Proteus' dislike of being captured and showing the future from Greek mythology.
- On page 9 and 10 of Ghostbusters Get Real Issue #4, Proteus' gift for prophecy from Greek mythology comes into play.
- Proteus appears on the front cover of the Ghostbusters: Get Real trade paperback.
- Ghostbusters Get Real
- Ghostbusters Annual 2015
- Ghostbusters International #1
- Ghostbusters International #9
- Ghostbusters Crossing Over #2
- Mentioned on page 21. 
- ↑ Street Thugs ghosts (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 15:53-15:55). Time Life Entertainment. Ghost says: "Proteus will see to that."
- ↑ Ray Stantz (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 18:56-18:58). Time Life Entertainment. Ray says: "Listen. Proteus is one of the primal gods like Gozer."
- ↑ Egon Spengler (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 8:49-8:53). Time Life Entertainment. Egon says: "Not really, though the concentration seems strongest in the Midtown area."
- ↑ Winston Zeddemore (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 6:24-6:26). Time Life Entertainment. Winston says: "This is as bad when Gozer was around."
- ↑ Egon Spengler (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 6:30-6:33). Time Life Entertainment. Egon says: "However, there is a common spectrography to the captured ghosts."
- ↑ Ray Stantz (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 6:34-6:37). Time Life Entertainment. Ray says: "You're saying there's a single source? A nexus for the activity?"
- ↑ Ananke (2015). IDW Comics- "Ghostbusters: Get Real Issue #1" (2015) (Comic p.16). Ananke says: "And you do have a special aversion to being captured. Was your plan, then, to catch them before they could seek you. Well, that certainly speaks to necessity."
- ↑ Proteus (2015). IDW Comics- "Ghostbusters: Get Real Issue #1" (2015) (Comic p.16). Proteus says: "I want to restore the natural order of the world. Common men are not meant to have power over gods and demons!"
- ↑ Egon Spengler (2009). The Real Ghostbusters - "Janine Melnitz, Ghostbuster" (1987) (DVD ts. 9:55-9:58). Time Life Entertainment. Egon says: "The statue is charged with so much ectonic force, it's able to resist our weapons."
- ↑ What Came Before! (2016). IDW Comics- "Ghostbusters International #1" (2016) (Comic What Came Before!). Line reads: "Now Janine DID throw a paperweight at his head first, but I think we can all agree that teleporting someone almost 7000 miles for that kind of thing is a gross over-reaction, even for a Class VIII primordial being."
- ↑ 68-R Memo (2018). IDW Comics- "Ghostbusters Crossing Over Issue #2" (2018) (Comic p.21). Memo reads: "PKE Reading: 16090525.15 ."
- ↑ Ananke (2015). IDW Comics- "Ghostbusters: Get Real Issue #1" (2015) (Comic p.15). Ananke says: "The Old Man of the Sea is not usually one to make requests."
- ↑ Turner, Patricia & Coulter, Charles Russell (2000). Dictionary of Ancient Deities, p. 391. Oxford University Press, New York NY USA, ISBN 0195145045. Line reads: "Proteus - Old Man of the Sea. His parents are Oceanus and Tethys. He is a prophet and shape-changer who herded sheep for Poseidon."
- ↑ Ananke (2015). IDW Comics- "Ghostbusters: Get Real Issue #1" (2015) (Comic p.16). Ananke says: "And you do have a special aversion to being captured."
- ↑ Ananke (2015). IDW Comics- "Ghostbusters: Get Real Issue #1" (2015) (Comic p.17). Ananke says: "For one who has been known to see the future, you're being remarkably shortsighted, Proteus."
- ↑ Narrator (2015). IDW Comics- "Ghostbusters Annual 2015" (2015) (Comic's Story So Far). Narrator says: "They even met other-dimensional versions of themselves, who were on the run from the primordial god Proteus, and the ensuing confrontation with Proteus left the Ghostbusters' Firehouse headquarters heavily damaged..."
- ↑ Egon Spengler (2015). IDW Comics- "Ghostbusters Annual 2015" (2015) (Comic p.3). Egon says: "The damage cased by our encounter with Proteus will require a massive amount of money and effort to repair."
- ↑ What Came Before! (2016). IDW Comics- "Ghostbusters International #1" (2016) (Comic What Came Before!). Line reads: "It was damaged during an extradimensional incursion by the god Proteus (as seen in the GHOSTBUSTERS: GET REAL mini series, where our heroes also met their counterparts from an alternate universe)."
- ↑ Janine Melnitz (2016). IDW Comics- "Ghostbusters International #1" (2016) (Comic p.13). Janine says: "Sweetie, I got zapped there by some blonde giant in a toga."
- ↑ Narrator (2016). IDW Comics- "Ghostbusters International #9" (2016) (Comic p. Dramatis Personae). Narrator says: "The Egon Spengler of an alternate reality that they had recently met during an altercation with a Class VII entity."
- ↑ 68-R Memo (2018). IDW Comics- "Ghostbusters Crossing Over Issue #2" (2018) (Comic p.21). Memo reads: "The Ghostbusters of dimension 68-R, the first we encountered, were thrown into this dimension while dealing with an entity known as PROTEUS."