A second example is Obsidian Entertainment's "", where the player's decisions influence whether one of three different factions gain control of the area surrounding post-apocalyptic Las Vegas. These factions include Caesar's Legion, a group of Roman-esque slavers; the New California Republic (NCR), an expansionist military government; and Mr. House, the enigmatic "de facto" ruler of New Vegas, in command of an army of robots that patrols the city. Each of the three sides aim to control Hoover Dam, which is still operational and supplying the American Southwest with power and clean, non-irradiated water; thus, control of the dam means effective control of the region. A fourth option, siding with a robot named Yes Man and prevailing upon or eliminating the other faction leaders, enables the player to go solo and take over the Hoover Dam for themselves.