|Yes! Scientifically speaking, that is who I am.|
Carlos is a Latino scientist who arrives (along with his perfect hair) in Night Vale in the first episode, "Pilot". He is described as having a voice like caramel with oaky tones, brown eyes, dark and delicate skin, black hair with a "dignified, if premature, touch of grey at his temples", and a strong, square jaw and teeth "like a military cemetery." By Episode 147, Carlos has grown a "very soft" beard with "two thin silver racing stripes down the chin". In the live show A Spy In The Desert Telly the barber describes the haircut he gave Carlos "he asked me for a light trim on the sides, and I misheard it as “shave asterisk in my sideburns, then cut me some bangs”. He wears a lab coat and appears in a later episode wearing a flannel shirt and well-fitting jeans. Although his age is unknown, the fandom seems to depicts him as somewhere in his thirties or forties. He drives a hybrid coupe.
Carlos first lived in or near his laboratory, which is next to Big Rico's Pizza on the outskirts of the science district, but later moved in with Cecil in an apartment in Night Vale. Cecil later states that they have moved into a house together after their marriage.
Like many characters in the series, Carlos's age is never explicitly stated, although he can be assumed to be of similar physical age to Cecil. Episode 55, "The University of What It Is", indicates that he's been active as a professional scientist for at least a decade. In addition, in Episode 146, it is mentioned that Carlos's double, Charles, is 41, which means that Carlos could be 41 as well.
Carlos's last name has never been mentioned, But is most likely "The Scientist".
Arrival in Night Vale
Carlos came to Night Vale in June 2012 in order to take a research fellowship at Night Vale Community College. It was intended to be a temporary appointment, but Carlos has seemingly settled in Night Vale permanently, and his home institution claims he's been missing for decades. He has an unexplained source of funding to support his laboratory, equipment, and studies. Nothing clarifies exactly what kind of science he studies, although in an email to Cecil, he says he is not a botanist or a dendrologist ("I am a scientist. I study science, not plants or nature.") Given that he calls Night Vale "the most scientifically interesting community in the U.S.," he is probably a student of anomalous phenomena along with his more traditional specialities.
Despite being an outsider, the citizens of Night Vale seem to accept and like Carlos. Jackie Fierro notes that his intense interest in science and his sometimes unorthodox beliefs are unusual in Night Vale, but she still thinks he's "nice". Jackie also appears to agree with Cecil's views on Carlos's attractiveness, stating that "there really was something blindingly handsome about him." in Welcome to Night Vale: A Novel. Diane Crayton thinks he is "well-spoken".
He initially leads a team of scientists who investigate various phenomena in Night Vale. Upon their arrival, the team's first action is to call a town meeting and explain their intentions to the residents, where Carlos tells everyone in attendance that Night Vale is the most scientifically interesting community in America and that they intend to study the strange goings-on.
Carlos and his team first investigate the nonexistent house in the Desert Creek housing development, and they ended up standing in the street in front of it, daring each other to go up and knock. In episode 3, they report that books have "stopped working." In "One Year Later", they were offering $5 to anyone willing to ring the doorbell on the nonexistent house, and in episode 30, "Dana", they actually offer this money to Carlos himself, but he refuses for reasons of "scientific integrity."
Carlos' voice is heard in "The Phone Call" and "Parade Day". In "The Phone Call", he leaves Cecil several messages on his voicemail about the clocks and the Man in the Tan Jacket outside his door, and in "Parade Day", he calls about the nonexistent house.
In "Company Picnic", a group of his scientists are arrested for trespassing on the house that doesn't exist by StrexCorp. However, Carlos, being inside the house at the time, doesn't get arrested, something that frustrates StrexCorp representative and Night Vale Community Radio manager Lauren Mallard, who already captured Cecil. This makes Carlos effectively on the run.
In "Antiques", Carlos makes himself appear in Cecil's broadcasting studio. Since he's not really there, (he is really in the Desert Otherworld), they can't touch, but they do talk. Carlos's conversation includes his desire to have Cecil come visit, and his scientific investigations.
In Taking Off, Carlos is studying how the phones can still work without there being a tower or without ever needing to be charged. He loses his years' worth of research due to Alicia and Doug's army constantly going out to fight other armies, who he proceeds to take care of. He appears in Kevin's studio, mentions the blood and tells him that he has to hand-deliver a letter and go to Night Vale for the last time.
In "The Protester", events in the Blood Space War caused Night Vale's timeline to be rewritten. One of these revisions to the timeline included changing the citizens so that many people who moved to Night Vale in the original timeline no longer did so. This change caused Carlos to be erased from history. 
In The Birthday of Lee Marvin (3) time is reset in nightvale to Carlos's amasement, as the clock he received from his mother is fully functional again he calls Cecil, who announces this live on air.
In "The Heist, Part 1" we learn that Carlos is working on a way to use fridges without opening doors, but the solution he is using is coating the kitchen in green stains that are hard to wash out, Abby Palmer and Steve Carlsberg allow them to stay in the shed in the back of their new house, and subsequently stains Janice's new car with a green handprint.
Unlike most of Night Vale's long time residents, Carlos is not blasé about the strange and horrible events that occur in the small town. These bizarre phenomena fascinate--and often frighten--him, and, especially in his first few months there, drive him to warn the residents, who don't seem nearly as alarmed as he is. For instance, on a visit to the radio station, he picks up radioactivity and follows it to Cecil's booth. Upon realizing that the radioactivity spikes highest around Cecil's mic, he gravely recommends that the station be evacuated. Of course, they cheerfully ignore this.
Ever pursuant of answers to scientific questions, Carlos apparently has to be reminded that he needs to give more importance to his own safety and other aspects of his life. Until "One Year Later", Carlos keeps his interactions with Cecil short and science-focused. After his near-death experience at the hands of the miniature city in the pin retrieval of Lane 5 at the Desert Flower Bowling Alley and Arcade Fun Complex, however, he finally does call Cecil for "personal reasons", and they go out on a date (during which they do experiments on trees and watch the rest of the town turn into buzzing shadows).
However, science remains central to Carlos's life. A lot of his brave and/or reckless behavior can be attributed to this, since it's often in the pursuit of science that he finds himself in dangerous situations. The aforementioned near-death experience came about because he went down into the underground city to investigate it (and also to prove that it was safe to do so in defiance of Teddy Williams).
In the process of studying The House That Doesn't Exist, Carlos discovers that someone can safely investigate as long as there are other people outside who can let them out. However, during his turn inside the house, his team gets arrested by StrexCorp, trapping him there, since there's no one on the other side of the door to open it for him. So he explores what later turns out to be the Desert Otherworld, which is so scientifically interesting to him that he delays coming home to Night Vale in favor of studying it for ten years (although Cecil and Night Vale experience only one).
Carlos respects and loves Cecil deeply, despite remarking that his boyfriend is "overenthusiastic" and "has very little grasp of science".
In "Voicemail", Carlos mentions that he likes "scientifically accurate jokes" and that he only tells those because he doesn't find the scientifically inaccurate ones funny. He also expresses interest in getting a tattoo with the definition of science ("I don't know, but I'm trying to find out, okay?"). It is implied that he regularly converses with the Masked Army about Cecil.
Carlos is loved immensely by his husband Cecil, who fell instantly in love with him during a town meeting soon after Carlos' arrival. Cecil speaks of Carlos often on his radio program, making no effort to disguise his open adoration, although Carlos often seems indifferent, or perhaps just unaware of Cecil's feelings. Whether intentionally or not, he's mentioned shooting down Cecil's requests for a date, usually just returning to his work.
Following a near-death experience one year after his arrival in town, Carlos shows that he does, in fact, reciprocate Cecil's affections, calling Cecil to meet with him in Arby's parking lot. The two share a tender moment, watching the sunset together while sitting on the trunk of his car,and later begin dating. They are currently in a steady relationship and got married in "Toast".
Carlos is aware early on of Cecil's job as the community radio host, and sometimes enlists his help in getting the word out to the town's people about strange or dangerous goings-on. Early in the show, Cecil tries to read a more personal message into Carlos's calls to the radio station. It is revealed in "Condos" that Carlos avidly listens to the radio show, stating that he listens "every time [Cecil's] on". It is implied that Carlos has been aware of Cecil's interest for some time, even from the beginning.
Carlos calls Cecil from the desert otherworld nightly and is vocally affectionate towards him. According to Cecil, Carlos is still of perfect face and hair, and the two regularly Snapchat, text, and run a Tumblr blog.
We still do not know many details of Carlos' life before his affiliation with the University of What It Is. In addition, the faculty members of the University of What It Is stated that he was missing for decades before they came to find him. While this might be due to the strange properties of time in Night Vale, it leaves a large gap in Carlos' history.
Resistance to mind control
On a number of occasions, Carlos has been unaffected by entities or effects that otherwise affected the entire town, Cecil included.
- Much of Night Vale turned into buzzing shadow entities during Carlos and Cecil's first date, but Carlos was not affected and indeed tried to find a solution.
- All of Night Vale was affected by the lethargy of the Lazy Day, but Carlos was quite industrious throughout.
- Carlos was immune to the Well of Night cult due to sleeping through its chanting.
- According to Old Woman Josie, he smells "of lavender chewing gum." 
- From the Horoscopes, we can assume that Carlos is a Taurus.
- His three favorite beans are garbanzo, kidney, and jelly.
- It is mentioned multiple times in the novel “It Devours” that Carlos is sometimes averse to touch (though not always, and sometimes likes to be touched in particular ways, such as having his ears stroked).
- Carlos stashes illegal writing utensils.
- He underwent throat surgery sometime before the events of "Condos", which caused his voice to notably change.
- It is revealed in "It Devours" that though the amount of time that passed in Night Vale when Carlos was trapped in the Desert Otherworld was equivalent to a single year, it was ten years in the Otherworld. Carlos confides in Nilanjana that he has yet to disclose this information with his husband, Cecil, in the fear that it would upset and worry him.
- Carlos did some theater in college and loves acting. He thinks he is very good at doing different accents (he is not).
- Carlos is allergic to cats and had to take medicine when Khoshekh was being kept at Cecil's house. 
- The ship between Cecil and Carlos is called Cecilos
- In A Spy In The Desert Telly The Barber describes the horrible haircut he gave Carlos "he asked me for a light trim on the sides, and I misheard it as “shave asterisk in my sideburns, then cut me some bangs.”
Behind the Scenes
Carlos was originally voiced by Night Vale co-writer Jeffrey Cranor. According to fellow Night Vale writer Joseph Fink, Lou Fernandez of Lou Reads the Internet for You is an experienced voice actor and was the first choice to play Carlos. However, it was decided that Carlos ought to be voiced by someone who could be called in at a moment's notice and Cecil Baldwin suggested that Jeffrey use his "expert voice" to play the part himself.
Cranor voiced Carlos up until December 2013, when it was decided that the show ought to seek out a new actor. With live shows becoming more popular and the voice actors being present in front of audiences and in the media, Cranor expressed his discomfort at the fact that he was a straight white man playing a gay Latino, when various Latino actors were available and could be paid to voice the part instead, and cited this as one of the reasons for the change. Dylan Marron was chosen.
- Episode 3 "Station Management"
- Episode 8 "The Lights in Radon Canyon"
- Welcome to Night Vale: A Novel
- Episode 72 "Well of Night"
- Episode 111 "Summer 2017, Night Vale, USA"
- Episode 51 "Rumbling"
- Episode 38 "Orange Grove"
- Episode 47 "Company Picnic"
- Episode 59 "Antiques"
- Episode 65 "Voicemail"
- Episode 70A "Taking Off"
- Episode 70B "Review"
- Episode 147 "The Protester"
- Episode 1 "Pilot"
- Episode 16 "The Phone Call"
- Episode 25 "One Year Later"
- Live show "A Spy in the Desert"
- Episode 55 "The University of What It Is"
- Episode 27 "First Date"
- Episode 35 "Lazy Day"
- Episode 4 "PTA Meeting"
- Episode 100 "Toast"
- Live show "The Investigators"
- Episode 44 "Cookies"