<Tr> <Td_colspan="2"> ← Previous Season 3 Next → Season 5 </Td> </Tr> <Tr> <Td_colspan="2"> List of Supernatural episodes </Td> </Tr> <P> The fourth season of Supernatural, an American fantasy horror television series created by Eric Kripke, premiered September 18, 2008, and concluded on May 14, 2009, on The CW . </P> <P> This season focuses on brothers Sam (Jared Padalecki) and Dean Winchester (Jensen Ackles) encountering angels for the first time in their lives as hunters of the supernatural; this marks the introduction of eventual series regular, the angel Castiel (Misha Collins). The angels intervene to rescue Dean from Hell and bring him back to life after he was trapped there in the third season finale "No Rest for the Wicked". They explain that they have arrived on Earth for the first time in thousands of years in order to prevent demons from freeing the fallen angel Lucifer from Hell, as Lucifer would then cause the Apocalypse . The demons are led by the Winchesters' enemy, and Dean's murderer, Lilith . However, it becomes increasingly clear that something is wrong with Heaven and that the angels have their own agendas . Despite an initially happy reunion, tension grows between Sam and Dean because Dean fears Sam's growing demonic powers and distrusts Sam's returning demonic ally Ruby (Genevieve Cortese). </P>

When did season 4 of supernatural come out