Warning: SPOILERS for Star Trek: Discovery Season 3, Episode 9 - "Terra Firma, Part 1"
Star Trek: Discovery season 3, episode 9, "Terra Firma, Part 1", introduced a mysterious new character named Carl (Paul Guilfoyle), but who and what is he? Carl met Commander Michael Burnham (Sonequa Martin-Green) and Emperor Philippa Georgiou (Michelle Yeoh) when they beamed onto the planet Dannus Five searching for a cure to the Terran villain's fatal illness. Carl is certainly not the human male he appears to be and his true identity could herald the return of the type of powerful space gods that often popped up in Star Trek: The Original Series.
Many Trekkers would naturally and automatically assume that Carl is a Q; the omnipotent beings were a staple of Star Trek: The Next Generation and the Q played by John de Lancie also appeared on Star Trek: Deep Space Nine, Star Trek: Voyager, and Q recently cameoed in Star Trek: Lower Decks. However, there are other clues sprinkled throughout "Terra Firma, Part 1" that may nod to a different explanation for Carl. Regardless, it's hard to believe the well-dressed, irreverent humanoid wearing a bowler hat, sitting in an Adirondack chair, and reading a newspaper in the middle of a barren ice planet is actually a native of Dannus Five, which had no life signs according to Burnham's tricorder.
Even more curiously, Carl sat next to a standalone doorway that he urged Georgiou to pass through so she could find the answer she sought for her condition. Georgiou is dying from her molecules decomposing as a result of both crossing over from the Mirror Universe and time-traveling forward 930 years to 3189. Although Carl offered no answers or explanations, only conundrums, Georgiou passed through the doorway, which took her back to the Mirror Universe of the 23rd century - a pivotal moment when the Emperor executed the Mirror version of Michael Burnham for treason. When Georgiou made her quantum leap to her own past, she left the Prime universe's Michael behind with Carl on Dannus Five, and "Terra Firma, Part 1" didn't reveal anything more about the mysterious doorway's gatekeeper.
This leaves Carl as an open question until "Terra Firma, Part 2" hopefully sheds light on his true identity. In the meantime, Star Trek's history has several examples of the type of cosmic entity Carl could be. In TOS, the Starship Enterprise commonly encountered all manner of ancient lifeforms with inexplicable powers, and Star Trek: Discovery has mimicked the TOS style of storytelling, especially now that the 32nd century is an unexplored, new final frontier. As such, Star Trek: Discovery could be bringing back TOS-style space gods with a modern spin. After all, it was Discovery's sentient computer, which merged with 100,000 years of data from an ancient sphere, that pointed Burnham and Georgiou to Dannus Five. This is also a clue to how old and what Carl could really be as he may be a revamp of a classic Star Trek concept.
A Member of The Q Continuum
The odds are very good that Carl is a Q. Several different members of the Q Continuum appeared in TNG, although John de Lancie's irrepressible troublemaker is the best-known Q. The Q have often taken an interest in humanity, and two Qs even posed as human beings and became parents to Amanda Rogers (Olivia D'Abo), who didn't know she was a Q until she became an adult working aboard the U.S.S. Enterprise-D.
Since it's not uncommon for Q to pretend to be humans, especially when interacting with other humans (or in Georgiou's case, Terrans), it's likely that Carl is a Q who took an unthreatening human form to coax the Emperor into crossing through the doorway back to her Mirror Universe's timeline. Carl also exhibits a Q-like sense of humor, love of speaking in riddles, and he clearly has a sense of humor since Georgiou and Burnham found him reading a newspaper with the headline "Emperor Georgiou Dies Horribly Painful Death". A final clue that Carl is a Q is the planet he was found in - Dannus Five - could be named for writer Richard Danus, who penned the TNG episode "Deja Q".
The Guardian of Forever
There's also a strong possibility that Carl is an evolved version of the Guardian of Forever, which appeared in the all-time classic TOS episode "The City on the Edge of Forever". The Guardian of Forever was a sentient donut-shaped time portal that the Starship Enterprise found on a long-dead planet, not unlike how Burnham and Georgiou found Carl on the barren planet Dannus Five.
An ancient time machine, the Guardian of Forever could send someone anywhere and anywhen. The fact that the Guardian of Forever was basically a giant doorway to the past or future could be a clue that Carl is a humanoid incarnation of the Guardian and the door he sent Georgiou through is an updated version of the portal that Captain James T. Kirk (William Shatner) and Mr. Spock (Leonard Nimoy) used to travel to 1930s New York City.
Introduced in the TOS episode "Errand of Mercy", which also was the first appearance of the Klingons, the Organians were incredibly powerful and possibly immortal incorporeal beings composed of pure energy and thought. However, they took the form of an agrarian humanoid society when Kirk, Spock, and the Klingons encountered them in 2267 after Organia was invaded at the start of a war between the Klingons and the Federation. Although Organians detested interfering in humanoid affairs, they used their awesome abilities against both the Klingons and Starfleet to prevent the war and impose a peace treaty. Carl may well be an Organian himself since an Organian may possibly possess powers over time as well.
A Metron
The Metrons were another impossibly powerful alien race Captain Kirk encountered in the TOS episode "Arena", and it was the Metron who forced the Captain of the Enterprise to memorably fight a Gorn on Cestus III. The Metron had the ability to control and manipulate energy, even across vast distances of space, and they even sent the Enterprise 16oo light-years away from their previous course. The Metron that Kirk personally encountered claimed to be 1,500 years old, yet Kirk remarked he seemed "more like a boy". As such, the Metrons are extremely long-lived and time-travel may be one of their abilities, so it's possible Carl could indeed be a revamped version of a Metron.
A Holodeck Hologram
It's also possible that Burnham and Georgiou never left Discovery or beamed to Dannus Five and, instead, everything they're experiencing is happening aboard a holodeck. As part of their retrofit with 32nd-century technology, the recommissioned U.S.S. Discovery-A now has its own holodeck, which was confirmed by the canonical log entry by Commander Jett Reno (Tig Notaro) in the @startreklogs Instagram. So it could be that Georgiou's encounter with Carl and her return to the Mirror Universe is all an elaborate holodeck simulation. How this could save Emperor Georgiou from dying isn't clear, but if everything is happening on the holodeck, it would place the Terran's fate in the hands of Discovery's sentient computer, which is dedicated to protecting the ship and everyone aboard.
A Prophet
When Burnham said that Dannus Five was near the Gamma Quadrant on the galactic rim, the ears of Star Trek: Deep Space Nine fans perked up. The Gamma Quadrant is the home of the Dominion but the Bajoran wormhole to that little-explored sector of space was the home of the Prophets. Although Starfleet identified Bajor's gods as "wormhole aliens", the Prophets are immensely powerful and mysterious non-corporeal beings who exist outside of space and time. Indeed, Captain Benjamin Sisko (Avery Brooks) was half-Prophet and he ascended to his destiny at the conclusion of DS9. Could Carl actually be a Prophet, which would be yet another nod to Deep Space Nine by Star Trek: Discovery?
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