Doom II, also known as Doom II: Hell on Earth, is a first-person shooter game by id Software. It was released for MS-DOS computers in 1994. The continuous 30 levels are divided into three episode-like sections, defined by their corresponding sky texture; UAC Underground/Outpost, City, and Hell. Immediately following the events in Doom, the player once again assumes the role of Doomguy. After defeating the Spider Mastermind, the marine finds a portal to Earth opened by demons. After returning to Earth, the marine finds that it has also been invaded by the demons, who have killed billions of people. The humans who survived the attack have developed a plan to build massive spaceships which will carry the remaining survivors into space. Unfortunately, Earth's only ground spaceport has been taken over by the demons, who placed a barrier over it, preventing any ships from leaving. The marine battles hordes of demons and is able to deactivate the force field, allowing the remaining humans to escape. Once all the survivors have escaped Earth, the marine is the only human left on the planet. Just as he sits down to await death, knowing that he saved humanity, the marine then receives an off-planet transmission from the survivors in orbit, who have managed to find out where the armies of Hell are coming from. The message reveals that the demonic base is in the center of the marine's own hometown. He then fights through the city until he reaches the base, but sees there is no way to stop the invasion on that side. He decides to step into the portal to try deactivating it from the other side, entering Hell. After fighting through the hordes of Hell, the marine reaches the location of the biggest demon he has ever seen, called the Icon of Sin (Baphomet). He kills the Icon of Sin by firing rockets into its exposed brain. Its death causes devastation on Hell, and the portal to Earth is sealed. The marine wonders where evil people will go when they die now that Hell has been destroyed, and reflects that rebuilding the world will be more fun than saving it as he begins his journey back home.