The First Fallen Human is, well Chara, also known by their full name
Charity "Chara" Dreemurr (They/It, 9-12 years old). They climbed Mount Ebott in the year 1915 (2015 in the Tempestonian Calendar, wielding a soul of Love, which the monsters picked up from old archives and adopted it as their own) to escape their home village,which was a cult & Chara was "deemed" an incarnation of its god, and was adopted by the Dreemurr Family. Stayed in the Underground for 3 years before dying due to self-inflicted Buttercup Poisoning. Wielded the Heart Locket & Worn Dagger.
The Second Fallen Human is the younger version of WTSC!Kris, full name
Kristan "Kris" Dreemurr (They/She, 7-14 years old) who grew up in the 1920s in this timeline, wielding a Soul of Patience, and was an abandoned orphan (for some infection that required them to wear a preventative bandage on their forehead), who never knew their parents & befriended another orphan of the name Efemena "Efe", the third Fallen Human. Kris got lost on the Mountain during Halloween, with what she wore being a Halloween costume.Stayed in the Underground for ~7 years>. Wielded the Faded Ribbon & Toy Knife.
The Third Fallen Human climbed the Mountain looking for Kris, and was technically killed before Kris was (by Asgore). Full name being
Efemena "Efe" Rose (They/Them, 13 years old), who wielded the Soul of Bravery, and stayed in the Underground for about 2 months, doing a Pacifist Route before getting sent to Asgore by the Royal Guards in SNowdin. They wielded the Manly Bandana & Tough Gloves.Not much is known about Efe's personal life, besides their parents having died in a war, and wanting to become a wrestler when they were older.
The Fourth Fallen Human,
Grace Rose (She/her, 17 years old), climbed Mount Ebott after being highly disappointed at being left out of the Graduation, a bearer of the soul of Integrity, and lived with an abusive mother. She stayed in the Underground for a total of 6 months and did a Neutral Route before getting caught by Gerson in Waterfall. She wielded the Dusty Tutu & Ballet Shoes.
The Fifth fallen Human,
Akio Sato (He/Him, 16 years old), climbed Mount Ebott looking for an ingredient during Cooking Class for Academy, a man with a soul of Kindness, and was never seen on the Surface Again. He did a Pacifist Route and stayed in the Underground for roughly a year. He was friends with most of the Monsters, and was known for his cooking skills. Upon meeting Asgore, he purposefully gave him his soul. He wielded the Apron & Frying Pan.
The Sixth fallen Human,
Rowan Lowe (She/Her, 14 years old), climbed Mount Ebott looking for the other humans & Akio, had a soul of Justice, and did a Neutral Route at first, before resetting to do a Pacifist Route. She was at first hostile towards the Monsters but changed her mind upon learning more, and stayed in the Underground for about 2 years (if counting the Reset). Like with Akio, she purposefully sacrificed her soul to Asgore. She wielded the Cowboy Hat and Empty Gun.
The Seventh and non-canon who only exists in When Timelines Collide human,
Fabian Maye (He/Him, 11 years old), got lost on Mount Ebott on his way back home from a Musical Performance, and stayed with Toriel for a while. If it weren't for him, the box of old human shoes & toys wouldn't be as filled up. He wielded a soul of Amity, and was in the Underground for about a month. Wielded a Costume Crown and Prop Scepter.
The Eighth fallen human,
Viola Athe (She/Her, 13 years old), was a lonely kid who had few friends, had a soul of Perseverance (or Ambition in human terms), and said friends were a friend group she was close to, namely Francine & Frisk. She, alongside Francine, got lost on a trail during the school trip Frisk missed out on, and a blizzard separated the two in the early Summer of 2010 (2110). She stayed in the Underground for half of a year, and accidentally fell into the Core after its completion, with the only intact piece found being her soul by the Royal Guards.
The Ninth fallen human,
Francisk "Frisk" Madisonia (They/He, 12 years old), had a soul of Stamina, missed out on a school strip their two friends vanished on, and was alone with their emotionally abusive father & loving but overworked Mother. One day, Frisk met Ezra, and the two formulated a plan to climb Mount Ebott to find their two friends in the summer of 2015 (2115). Frisk ended up getting separated from Ezra, their half-sibling, and fell Underground. In this timeline, Frisk did a Neutral, later Pacifist Route, and ended up leading to the Destruction of the Barrier. Their starting gear was a Bandage and Stick. An encounter with a certain butterfly allowed them to change soul modes at will, with Red being the default mode. Somehow, the last fallen human strangely resembled the first.
(Yes, I know Undertale isn't set in 2015 and instead a future year, but I'm changing it on purpose & having it that Monsters used a different calendar than the Humans.)