Chara

Chara was the first human to fall into the Underground. Injured from the fall, they were brought back to the castle by Asriel Dreemurr, and was quickly adopted by the Dreemurrs. Years later they died from self-inflicted Buttercup poisoning.

After the 8th human, Shae, fell into the Underground, they became her narrator and their LV got linked to hers. They have been by her side ever since and offers guidance and acts as her guardian angel of sorts.

Appearance
Chara is a human child seen to be wearing a lime and cream-colored striped shirt and red-brown pants and shoes. Chara has peach skin and red-brown hair, rosy cheeks, and red-brown eyes. They are seen wearing a golden heart-shaped locket given to them by Asriel. They treasure it dearly.

As a ghost, Chara is often partially transparent, but can phase in and out at will.

Personality
Chara is a sympathetic, smart, and wise child who loves chocolate to the point of it being almost comical. They can often come off as abrasive and sarcastic, but is kind at heart with the right intentions. They also show a more sensitive to them as they seem to be touchy about how they treated Asriel sometimes and their potential to turn evil due to their LV sometimes fluctuating if they are angry or distressed, despite their LV being directly tied to Shae.

They despise humanity due to the humans' cruel nature, which is shown when they were suspicious and wary of Wyatt and Daniel. Despite their hatred towards humanity, they developed a soft spot towards Shae once they warmed up to her. They seem to be warming up to Daniel as well.

Pre-SHAETALE
A long time ago, Chara climbed Mt. Ebott for unknown reasons, but Asriel states that it was for "Unhappy reasons", heavily implying that they were either contemplating suicide, or was trying to just explore the mountain and get away from their bad home environment, and tripped and fell into the Underground. Found injured by Asriel, they are taken back to the Dreemurrs' castle. They are quickly and happily adopted by the Dreemurrs. Chara grows closer with them all, forming a close friendship and sibling bond with Asriel. Chara became the future HOPE of monsters and humanity.

One day, they formed a plan with Asriel in which they'd commit suicide and would allow him to take their SOUL to break the BARRIER. Chara purposely ingests buttercup flowers to fatally poison themselves. Chara's last wish was to see the flowers in their home village. Eventually, they die. When their SOUL fuses with Asriel's they form a powerful hypergod fusion, and they pass through the barrier, making their way towards the village. When they got there, the humans thought Asriel had killed Chara, having seen him carrying their dead body. The humans attack him. Chara attempts to fight back, but Asriel holds back, overall not fighting back. Fatally wounded, Asriel makes way back, and collapses in the throne room, turning to dust; the plan was a failure.

Shae
Chara serves as Shae's narrator. At first, Chara was hesitant about Shae, but quickly grew fond of her and began trusting her. They grew close to her to the point of seeing her as a sister figure or even a parental figure.

Asriel / Flowey
Chara and Asriel are best friends. When they fell into the underground, Asriel helped them back to the castle. The two quickly grew close and were nearly inseperable. Around when they began their plan, their relationship seemed to have become tense. After their suicide, Chara felt betrayed by Asriel for refusing to attack the humans, and began feeling nothing but hate and resentfulness, but years of being a ghost made them realize they were in the wrong and didn't blame Asriel for not going through with the plan, but instead began resenting themself for manipulating him to do such a plan.

When they became Shae's narrator, they assumed Asriel would want nothing to do with them. They know that he is Flowey, and has mixed feelings about him. They feel anger when they see Flowey and will angrily declare that he's not Asriel due to him not acting anything like the Asriel they know.

Sans
Chara and Sans have a playful rivalry. The two often bicker with each other and do playful jabs at each other. Despite hearing their past, Sans doesn't hate them nor hold it against them.

Trivia

 * Chara being the narrator is a popular UNDERTALE theory that has been around for a long time. There is also plenty of evidence to imply this.
 * Chara stays by the side of whoever has the most DT at the moment.
 * Typically, this means they're with Shae, but if her DT fell too low, they would be 'transferred' to whoever has the 2nd most.
 * Like Sans, Chara is left handed.
 * Chara says "Greetings" like Toriel does.