Here’s how The Vampire Diaries season 4 episode 23 revealed who Silas really was. Silas was a looming presence over much of The Vampire Diaries’ fourth season, even before he made his first physical appearance in the show. He was introduced by Professor Shane during a presentation at Mystic Falls High School during which it was revealed Silas was the world’s very first Immortals and a legend prophesized his return.
Further backstory revealed that thousands of years ago Silas asked his lover, a powerful witch called Qetsiyah, to create an elixir that would grant him immortality. After discovering Silas intended to use it on himself and another woman, Qetsiyah killed his side piece and buried the now immortal Silas alive on an isolated island. Qetsiyah buried a cure for immortality with Silas hoping he’d take it and die to be reunited with her on the Other Side, a sort of purgatory for supernatural beings. As revenge for Qetsiyah killing his other lover, Silas refused to take the cure until he was awoken from his millennia-long slumber by Katherine Pierce who took off with the cure.
After Silas rose again, it transpired he planned to destroy the Other Side and take the cure so he could be reunited with his one true love who wasn't Qetsiyah. However, at this time Silas’ true form was unknown. Before waking, a mask covered Silas’ face and after Katherine revived him he took on the form of various Mystic Falls residents to manipulate people into helping him. The Vampire Diaries season 4 saw Silas first pose as Professor Shane who had died on the island and he later took the form of Stefan, Damon, Rebekah, Caroline, and Klaus but never revealed what he really looked like.
When Bonnie petrified Silas into a stone statue, it seemed like his identity might remain a secret forever but in The Vampire Diaries season 4 episode 23, the truth was revealed. Stefan was about to throw Silas’ petrified body in a quarry but found that his body was missing. Silas rocked up in Elena’s form and explained that when he became immortal, Nature created a version of him that could be killed – a doppelganger.
As Silas had taken on Elena’s form, Stefan assumed he was a Petrova doppelganger until Silas revealed his true face – and it looked an awful like Stefan’s. It turned out Stefan was Silas’ shadow self just before the latter stabbed Stefan with a stake, locked him in a safe and sent him to a watery death in the quarry. More of Silas’ backstory and true intentions would be revealed, but The Vampire Diaries fandom would have to wait until season 5 to find out.