Sam Ester is an alternate version of Sam Winchester. Unlike his counterpart, Ester is a true demon that is trapped in the body of a human due to a spell made by Lilith, to make it easier to kill him when Sam agrees with Dean Winch to help the latter find a demon in exchange for his soul.
Sam is at first cruel and uncaring, only thinking about completing his deal and claiming Dean Winch's soul. However, over time he develops a bond with Dean, which the latter notices; however Sam shrugs it off as he simply want's his soul in good condition. But he abandoned this, and his demonic heritage, when he killed Azazel, his father, to save Dean. This shows that his human experience has slowly transformed him into a noble demon.
Sam is a natural born demon. This means he never began as a human and completely originated from hell. Unknown to him, he is the son of Azazel.
For over two hundred years he tortured humans and demons alike, earning the darkest of all reputations.
When he went to Earth for the first time in 1987, he encountered John Winch and his girlfriend Mary. He also encountered the time traveling Dean Winch and, unknown to him, his future self. This adventure was erased by Castiel Winch when he regained his Grace, meaning Sam was unable to remember the adventure.
Meeting Dean for real
The seeds of humanity
Killing Azazel and temporary death
Two years on Earth; Two hundred in hell
Infamous for being the fourth most evil being in the world, Sam was a ruthless and heartless being, even by demon standards. He fancied himself an artist, finding new and spontaneous ways to torture souls.
When he becomes human, he is disgusted and angry at all the things humans require, such as food and sleep and going to the bathroom. He is also more focused on completing his deal, which will restore him back to his demonic glory. He also shows disdain and annoyance towards all humans, Dean especially. He didn't care about Dean other than claiming his soul.
However, his life changed forever when Dean saved his life, making him feel a pure emotion for the first time: gratefulness. Quickly, Sam found himself experiencing new emotions, including love when he met Jessica. This also made him reconsider everything in his life and to feel guilty for his actions in hell. Also, he found himself respecting Dean and finding himself to be treating Dean like an older brother as they saved lives and fought evil.
These experiences led to him renouncing his demonic heritage and killing Azazel. After telling everyone how he felt about them, calling Dean the greatest friend he could have ever asked for, Sam found the humanity in him to sacrifice himself to close a gate into hell.