Who is Sierra in Overwatch? Sierra, formerly known as Hero 51, has been officially revealed with the release of the Summit Breach trailer, giving us a first look at the newest character in Season 2. As a member of Helix Security, Sierra utilizes a large plasma rifle and a bird-like drone to protect the world from evil forces. While the Overwatch trailer didn't reveal as much as we would've liked, there has been a leak that confirms some suspicions people have about her kit. With Season 2 set to launch on April 14, we won't have to wait long to see where Sierra fits alongside the best heroes on the Overwatch tier list.