The humble beginnings of a great evil
Anakin Skywalker was born on the backwater desert planet of Tatooine in the year 41.9 BBY (Before Battle of Yavin) to hereditary slave Shmi Skywalker and an unknown father. Rumors and legends say that Shmi conceived Anakin through "midi-chlorians" or the Force but this is baseless conjecture and obviously impossible. Without any father figure in his life besides his cruel slave masters, Anakin turned to mechanical engineering for comfort by building his own companion droids out of stolen parts.
Eventually found by Queen Padme Amidala of Naboo and her escort Jedi Master Qui-Gon Jinn, Anakin unknowingly earned his freedom by winning an illegal hover race for the Jedi Master. Now adopted by the Queen and the Jedi Order, Anakin was forced to abandon his mother and only family in the hopes of having a better life.
However, Anakin was not to find peace on Coruscant with the Jedi Order. Immediately thrust back into conflict alongside his Jedi Master Qui-Gon Jinn, Anakin participated in the Battle for Naboo as a child soldier and is reported to have killed thousands by destroying a Trade Federation space battleship. By the age of 13 Anakin had personally killed more people than any serial killer in the history of Earth; a record that would only be broken by his son Luke when he destroyed the Death Star, killing hundreds of thousands of Imperial Navy personnel.
These were not traumatic times for Anakin as he took to his role of warrior very well under the tutelage of former colleague, now Jedi Knight Obiwan Kenobi. Qui-Gon Jinn declared Anakin "The Chosen One" to the Jedi Council before his death, cementing the desire for superlative that would define Anakin as an adult. As such, he was treated with special privilege by the Jedi Order and seemed to thrive, becoming a model Jedi padawan by the time of his early 20's.
As he grew older and more experienced Anakin began to follow his new Master Obiwan Kenobi on more and more dangerous missions. Eventually Anakin took part in the events on Geonosis that started the Clone Wars between the Galactic Republic and the Confederacy of Intergalactic Systems. Anakin took to wartime like a fish to water, gaining glory and prestige to feed his ego with. Even with the loss of his arm in battle and its subsequent replacement with a robotic prosthesis Anakin lost none of the ambition that his early childhood had trapped him in. It was during this time he began his affair with the women who adopted him, Queen Padme Amidala. The two would carry a life long yet hidden relationship and this would arguably be one of the main causes of Anakin's descent into evil.
The period just before and during the Clone Wars is when Anakin's sociopathic tendencies became apparent. He grew more aggressive and this mixed with the proud ego that had been fed by so many during his formative years after leaving slavery. Starting with the massacre of a village of native Tuskens on Tatooine in revenge for his mothers death at their hands, the true evil of Anakin Skywalker starts coming to light at this point in his life.