Theo is a supporting character in Celeste, who climbs the mountain alongside Madeline. He is an aspiring photographer who climbs Celeste Mountain primarily to take pictures that will boost his followers on InstaPix, and acts as a companion to Madeline on her journey. He appears at various points in the story to speak to Madeline as well as assuming a more active role in the story from the end of Chapter 4 to the beginning of Chapter 6.
Theo is a tall Brazilian-American man with a dark brown skin complexion, brown eyes, and curly brown hair with a large beard. Throughout the game, he wears a green checkered coat, dark blue pants, a yellow scarf and a brown backpack. He has a several tattoos; two circle designs on his shoulder, a feather on his neck, and a floral design on his forearm.
Theo is a laid-back, friendly and happy-go-lucky young man, with an obsession for social media. He loves taking pictures, and just wants to have fun exploring Celeste Mountain. He often does "goofy" things during the course of the game, such as falling face-first off a small cliff to reunite with Madeline (in Chapter 4) and randomly taking mirror selfies in an ancient temple (in Chapter 5).
Despite being somewhat of a comic relief, he also displays maturity towards wanting to get the most out of his life and acts as emotional support for Madeline during the climb.
Theo lived in California for a while before moving to Seattle, where he got a job he hated. The type of job is never specified. He eventually quits and moves again to Vancouver, Canada; hitchhiking there. He then decides to visit Celeste Mountain, due to his recently deceased grandfather (vovô) having travelled there.
In Chapter 3, he enters the hotel before Madeline, and is frightened by Mr. Oshiro. During the Huge Mess section of the chapter, he can be seen trying to pull the grate off an air vent in the laundry room when Madeline encounters him. He tells Madeline that Mr. Oshiro could be dangerous and that she should escape the hotel along with him, but she declines, wanting to help him clean up. After this, Theo crawls through the vent alone to escape.
In Chapter 4, Theo encounters Madeline once again, by rather comically falling off a small cliff. He rides the Gondola with Madeline, talking with her for a while, and then taking a selfie. However, the Gondola suddenly stalls out and lurches (caused by Badeline), and Theo accidentally breaks the lever. This sends Madeline into a panic attack, but Theo successfully calms her down by teaching her a breathing exercise involving a floating feather (controlled by the player). The Gondola then resumes, and Madeline thanks Theo for helping her calm down. They both laugh at the terrible photo that resulted from the lurch as Chapter 5 begins.
At the beginning of Chapter 5, Theo rushes into the temple, excited to explore and take photos, despite Madeline's protests. After taking a mirror selfie, he becomes stuck inside the mirror, and eventually winds up trapped in a crystal, made out of his own psychic energy, unable to move. Eventually Madeline arrives and carries him out of the temple.
At the beginning of Chapter 6, Theo has a long conversation with Madeline regarding their origin of their mountain climbs, why they decided to do it, and what personal struggles they are dealing with. He also tells her about his sister - Alex, who has a lot of similarities with the main protagonist. After that, they both take a selfie as a way to remember their conversation, and go to sleep. He later wakes up during Madeline's encounter with Part of Herself. After she falls, Theo runs down to the cavern to find her. He later appears at the end of the chapter, relieved that Madeline is unharmed, and remarks that Badeline looks like "an adorable goth Madeline".
He later appears during the Epilogue, waiting for Madeline at home with the rest of their friends. Madeline later bakes a pie for them, and his reaction depends on the amount of strawberries the player has collected.After that Theo doesn't appear very much, apart from a small conversation with the Old Woman during Chapter 8, where Madeline says that he visited Vancouver during the summer in which they spent some quality time together, and that he's now back at home to support his family. For the last time he's seen during the last cutscene in Chapter 9, where he appears in a video call, asking if Madeline is feeling any better after her loss. He shows her a photo he found of the Old Woman with his grandpa, revealing that they must have been close friends, much to her surprise.
"Nailed it." - Chapter 4
"YOLOOOOOOOOO!!" - Chapter 1
"Selfies are always worth it, dude." - Chapter 1
"Madeline, you just saved my life. That's not pointless." - Chapter 5?
- Theo's Instapix account, theounderstars, is a real Instagram account. It follows Theo's everyday life before, during and after the events of the game, and he even responded to some comments on his posts.
- Despite adding a filter to his and Madeline's first selfie in-game, the picture posted onto Instagram itself has no filter.
- Theo's family is from Brazil.
- During the events of Chapter 5, while trapped in the crystal, Theo is surrounded by eyes that are perpetually staring at him. It is unknown whether this represents some form of anxiety (similar to Badeline and the Seekers) or just a simple fear of being stared at.
- If you name Madeline “Alex,” then Theo’s sister will be named Maddy, most likely short for Madeline.
- If you don't interact with Theo in Chapter 1 or 2, Madeline will ask theo if he is a guest in chapter 3 where you have to talk with theo then they will introduce themselves like in Chapter 1.
- Theo's Instagram: "SEATTLE SELFIE!"
- Theo's Instagram: "Spoons opened the sock drawer"
- Theo's Instagram: "Going back home now"
- Theo's Instagram: "Good morning!! 🌞 Spoons says hi too!"
- Theo's Instagram: "Best summer of my life."
- Theo's Instagram: "I caught up with Maddy, it's all good."
- Theo's Instagram: "I quit. I couldn't stand another day of that. Maybe I'm just not cut out for a real adult career. Peace out Seattle, I'm going to Canada!"
- Theo's Instagram: "Almost there! Hitchhiking with these adorable locals."
- Theo's Instagram: "Met this nice old lady today! #newfriend"
- Theo's Instagram: "Me and my new BFF Madeline!"
- Theo's Instagram: "#tbt my fave pic."