Springtrap on EthgoesBOOM's channel is much different than his canon counterparts (books and games). This is shown by the fact that he actually cared for his children, and wanted to redeem himself/change his ways. The animatronics learned this in this video, and now accept him as part of their crew. (I'll talk about it down below)
Little is known about his past. All we know is that he had a spouse and 3 (maybe 4, it's not really clarified) kids. As said above, he cared deeply for his family, and was devastated when his children died. This could possibly be the reason why he snapped. His name was William Afton and two out of his children were named Micahel Afton and Elizabeth Afton.
William Afton also worked with his business partner, Henry, to create the first restaurant that started the whole franchise, Fredbear's Family Diner. The two of them built animatronics to entertain children inside, those being Fredbear and Spring Bonnie. (It's true that Springtrap was once Spring Bonnie, but it is unknown in the canon games whether Fredbear is Golden Freddy. On this channel, they are the same entity.) The Diner soon shut down after William's youngest son was bitten on the head by Fredbear, also known as the Bite of 83. The events of FNAF 4 happen the same year (because Williams son is scared of the animatronics after the bite, he is in a coma and faces off against the Nightmare Animatronics before he sadly dies)
He also created Circus Baby's Pizza World, where the Funtime animatronics were made. These animatronics were: Circus Baby (and her Bidybabs), Ballora (and her Minireenas), Funtime Freddy and Bon-Bon, and Funtime Foxy. This is where the death his of only daughter, Elizabeth, took place. Despite Afton warning her not to go near Circus Baby, she was attracted to her (Not like that you filthy sinners), and was stabbed by Baby's scooper/grabber thing and disappeared. This lead to the events of FNAF: Sister Location.
Back on the topic of Afton going insane, Freddy Fazbear's Pizza soon arrived to replace Fredbear's. This is where William killed his first victim: Henry's Daughter, Charlie, who became the Puppet. He then killed many more children, who the Puppet gave life to by stuffing their bodies in Freddy, Bonnie, Chica, Foxy and Golden Freddy. Because of this the first location of Freddy Fazbears Pizza closes down and the animatronics become Withered. In 1987, Fazbear Entertainment opens up the 2nd location of Freddys featuring Toy Freddy, Toy Bonnie, Toy Chica, Toy Foxy(later known as Mangle), BB,JJ and the Puppet as well as the Withered crew. Here, William strikes again killing five more children who, thanks to the Puppet, go on to possess the Toys and BB.(the events of FNAF 2 happen) Because of this, the infamous Bite of 87 happens when one of the animatronics (most suspect either Mangle or Foxy) bites out someones Frontal lobe. Due to this the Toys are scrapped and the place closes down. The Withered crew is repaired and upgraded to some extent. Then in the early 90s Freddy Fazbear's Pizza reopened (to be exact the 3rd location) with Freddy, Bonnie, Chica and Foxy (And Golden Freddy in the shadows). In 1993, the events of FNAF 1 happen.
After the events of FNAF 1 but way before FNAF 3, Afton started to use a disguise called Shadow Freddy. He lured the animatronics to the back area of the pizzeria, and then destroyed them so he could cover his tracks. Little did he know this released the sprits of his victims. The spirits of the dead children soon got their revenge, scaring William to hide in the Spring Bonnie suit. At first he thinks he is safe and starts laughing but due to his movements and the poor condition of the suit, the Springlocks snap loose and crush/impale him, killing him. This is how he became the animatronic we know as Springtrap.
After 30 years of decaying in the backroom, Springtrap resided in Fazbear's Fright, with his one desire to get revenge on the animatronics for trapping him in his robotic tomb. He tried to change himself for the better, until he played The Littlest Penguin, which sparked his interest in killing again. After this scenario, he meets Plushtrap, who wishes to work with him. Springtrap laughs at him and Plushtrap swears his revenge, beginning their rivalry.
Springtrap then proceeded to destroy Freddy, Chica, Foxy, Mangle, BB and The Puppet, leading to the events of FNAF 3 (Also known as the Fazbear Massacre.) Bonnie, Toy Freddy, JJ, and Plushtrap work to stop this insanity, until they realize they got a Bad Ending while doing so. Golden Freddy then steps in to complete Night 6 and stop the madness once and for all. After this night, Springtrap sets and fire and he burns down the attraction. (RICH SET A FIRE AND HE BURNED DOWN THE HOUSE, wOAhoAH) The animatronics start to grieve, thinking that Golden Freddy also burned in the fire, until the hero (which was him) escaped. After said fiasco, they went back to 2016, locked Springtrap inside the safe room yet again, and threw away the key.
Soon, Christmas time comes around, and the animatronics start to celebrate. Springtrap sits in the back room, depressed as he thinks about his children. While they celebrate, JJ hears crying through the vents, and goes to investigate. She sees Springtrap, and after a long talk, JJ decides to convince the other animatronics to let him free, which they agree to do. This is the start of his redemption.
It first started out by helping the others decorate, but then, Springtrap started playing more games, and has eventually become a part of the Fazbear crew.
Note: What you see ahead in somewhat canon lore for FNAF 6. This has not been shown in the EthGoesBOOM universe (On camera, at least). The only evidence are episodes that include Scraptrap, Scrap Baby, Lefty, and the Rockstar Animatronics. Also, spoilers.
Sometime after the events of FNAF 3 but before FFPS, after the fire at Fazbears Fright Springtraps suit was left in heavy disarray so he went to an old location of Freddys and used parts of an Old Spring Bonnie suit to repair his own. He became Scraptrap.
Then during the events of FFPS (Fnaf 6), He was lured by his old business partner, Henry, to what would be the last location of Freddy Fazbears Pizza (the FFPS location with the Rockstars, Mediocre Melodies, Trash and the Gang, Security Puppet, Helpy and the Posh Pizzeria). There he reunited with his daughter who now went by Scrap Baby after she was ejected from Ennard by the others for "Being too bossy". As for Ennard, Funtime Freddy took over the body and he now went by Molten Freddy. It is assumed Scraptrap and Scrap Baby were very happy to be with each other again and Scrap Baby wanted to even follow in her father's footsteps and become a killer as well. Over the course of the week, Scraptrap, Molten Freddy, Scrap Baby and a new Animatronic named Lefty (who, in reality, is the Puppet in disguise because Lefty was designed to trap the Puppet) were salvaged by Scraptrap's own son, Michael Afton ,who was now working with Henry to finally bury his father's tragedies over the years (seeing how these four Animatronics were the last ones who were possessed). By the end of the week, when Scrap Baby was about to kill Michael after saying "I will make you proud Daddy!" Henry soon interrupts her and tells them all his plan, that he will set fire to the restaraunt and burn all the Animatronics, in order to release their souls. He then says "And to you Monsters trapped in the corridors, be still and give up your spirits.. they don't belong to you. For most of you, I believe there is peace and perhaps something more, waiting when the smoke clears. But as for one of you, the darkest pit of hell has opened to swallow you whole, so don't keep the devil waiting old friend" he is basically damning William to hell because of his past crimes. He then begins to address Lefty (the Puppet) as his daughter and apologizes for not being able to save her when William killed her. The Pizzeria then burns down with all the Animatronics, Henry and Michael in it, killing them all and releasing their souls. Henry and Charlie go to rest together, Michael and Elizabeth reunite with their brother (FNAF 4 child) but as for William he now has to spend all of eternity in hell for his past crimes.
But now, thanks to lots of evidence as of late, this might not be the end of William Afton's story. Set after the events of FFPS (FNAF 6), Ultimate Custom night could In fact be William Afton's hell. Having to face off against his own creations for all of eternity, dying over and over never being able to feel peace. As evidenced by the many lines the Animatronics say to you upon dying, the OMC Minigames where OMC says "Leave the Demon to his demons" and how if you speed up the background noise you will hear what sounds like William screaming for his life. So, Henry was right, the darkest pits of hell had opened for him.
Note: Although this description has some canon things in it, most of this post was from Eth's channel. The Book William Afton is a douche, and not much about the game William is known except the fact he had a family, was business partners with Henry and that he killed Children.”Chica's... breaking her own neck, apparently.." -While playing One Night at Freddy's