Only a select few know of him and only a tiny few of them know him personally. He's been known to help but also to cause havoc.
Only his closest friends know what happened before the Omega Timeline was created. Most of his early life is a mystery. Though from one of his close friends its told that Human Sans had a family before W.D Gaster adopted him. The parents practiced traumatic practices on Human Sans for 5 years before the parents were killed in a supposed "accidental" house fire. From what is known after that is all standard for a Sans. Until the human arrived and Human Sans left his timeline after a genocide run in which he trapped the Monster in a state where they could not reset or continue and they were stuck on the start screen. But he could not reset either,therefore he waited as he could not escape the timeline or his AU. He explained that one day he followed an Error Sans through a portal leading to the Omega Timeline. There he stayed. He would be seen walking around Snowdin with a company of Frisk's or Sanses. He now walks alone as his friends have all passed,leaving him walking down this path he took,alone.
During Human Sans travels through the Omega Timeline, he met up with HugTale Frisk after getting dangerously hurt. HugTale Frisk healed him and they quickly bonded together and became friends. Human Sans grew a romantic affection for the Frisk but as HugTale Frisk already had a romantic partner, Human Sans had to move aside this feelings until when he revealed them. They share a close relationship but HugTale Frisk affection to Human Sans is more sisterly than Human Sans more romantic affection. During their friendship,they have gone through many hard times but they have always stuck together and gone through it, always being there for each other.
Human Sans does not see himself in the brightest light. He usually puts himself down and he focuses more on his mistakes than his success. He saves people from worrying by constantly lying about his mood.He has shown himself to care immensely about his friends and people he considers family, he would rather sacrifice himself then let others die instead. He has shown to have little self confidence and self value.
Not much is known about the relationship between Human Sans and his brother though he had shown considerable sadness over the death of his Brother many years ago and refuses to talk about it.
Unnamed big sister
: Human Sans has shown to only his closest friend,his relationship with his Unnamed older sister. He has shown during a memory showing to HugTale Frisk that he had a very close friendship with his sister and cared deeply about her. Ultimately causing a traumatic experience during her death on a bus crash where she protected Human Sans but died doing it.
The two at first got along quite well, Frisk even developed a crush on him. He didn't have any romantic feelings for her but that was probably because she had a boyfriend at the time. After a while they started calling each other Brother and sister. They both have their disagreements but he is generally kind to her.
Angel Void Frisk:
When they first met they were friends even romantic partners at one point but after a break up.Angel Void Frisk despised him and would always act aggressively towards him. Though the last time they saw each other She seemed quite nice to him which confused him as he expected a aggressive attack . She has shown some guilt over when he died,blaming herself for letting him die.
She hated him at first but after some time they became a couple. She loved being with him. But the romance didn't last long due to Shade Sans possessing him and causing havoc, leading to Teen Frisk suicide. She was later revived by Human DeathTale Sans.Teen Frisk tried to get back with Human Sans but he didn't want to hurt her again and he tried to get her to find someone else. She got with Themus and she forgave him. He still feels guilty about leaving her.