Here's how the fallen angel Gadreel is sort of the main character of Supernatural season 9. The CW's Supernatural debuted back in 2005 and follows the adventures of the Winchester brothers, who were raised by their father John, played by Jeffrey Dean Morgan (The Walking Dead), to hunt supernatural beings like demons, ghosts, and assorted monsters. The show's combination of buddy comedy with creepy horror quickly saw it find a cult fandom.
While the show's creator envisioned it running for about five seasons max, Supernatural has surpassed everyone's expectations by lasting fifteen seasons. The Winchester brothers have been to Hell and back - literally and figuratively - many times over the course of the show's 300 episodes, and fans will be sad to see it come to an end in 2020. The show also spawned an animated spinoff with Supernatural: The Anime Series in 2011.
Supernatural season 9 opened with Sam Winchester, played by Jared Padalecki (Friday The 13th), in a coma following the events of the previous season. In desperation, his brother Dean (Jensen Ackles) calls on an angel to save his life. Dean lets the angel Ezekiel possess his brother in order to heal him and promises to keep the possession a secret from Sam. It turns out the angel isn't actually Ezekiel, however, but Gadreel, the former guardian of the Garden of Eden. Gadreel failed to stop Lucifer gaining entry to the Garden, indirectly leading to minor events like the corruption of man and the creation of demons and Hell. Gadreel was tortured endlessly for his failure and is seeking to redeem himself during Supernatural season 9.
Gadreel teams up with Metatron, played by Curtis Armstrong (Happy!), to help him rebuild Heaven. While he serves as an antagonist for much of Supernatural season 9, Gadreel ultimately becomes a hero in the finale "Do You Believe In Miracles?", sacrificing himself to help stop Metatron. In the way it could be said Thanos is the technically the main character of Avengers: Infinity War, it could be said Gadreel is a key protagonist of the ninth season. He possesses Sam himself for about a third of the season and is played by actor Tahmoh Penikett (Man Of Steel) for the rest of the series.
Gadreel is one of the most tragic characters of Supernatural, with his one mistake having gigantic consequences. In season 9 he was willing to commit dark acts to try and undo their failure but after he saw the error of his ways, he willingly sacrificed himself in order to help the heroes save the day. In terms of fan favorite Supernatural villains, Gadreel doesn't have the popularity of characters like Crowley or even Lucifer, but he's undeniably one of the most important.