General Lee Oliver is the commanding officer of the New California Republic in Mojave Wasteland and one of possible antagonists of Fallout: New Vegas. While the NCR as a whole is deeply flawed but definitely well–meaning, General Oliver is a corrupt glory–hound who wants more than anything else to be remembered as a hero and pursues bettering his own image at the expense of soldiers' lives. His military strategies are naive and apparently poor and counterintuitive, and disapproved of by many NCR men seen in–game (most notably Chief Hanlon).
Oliver himself does not appear in–game until the final battle. In three out of the four endings, he is the very last opponent encountered before the game ends, appearing after you defeat Legate Lanius in both the "neutral" (Mr. House and Yes Man) endings and being the main antagonist (alongside President Kimball) in the Caesar's Legion ending. In the former two, he initially thinks that the player has won the Hoover Dam for the NCR but the player can either tell him their true intentions and attempt to make him surrender peacefully or attack him outright. Due to his stubbornness, General Oliver can only be successfully reasoned with if the player has a maximum Speech skill of 100. Otherwise, he and his men will attack only to be gunned down by an army of Securitrons behind them.
In the NCR ending, he's the one who orders the player to defend Hoover Dam from the incoming horde of Legionaries and finally attack the Legate's camp. He's also the one who congratulates the player after NCR wins the battle.
In the Legion ending, Oliver is not a boss character like Lanius but puts up more of a fight than in the other two endings, being fought in his personal quarters without any Securitrons where he is aided by numerous soldiers and traps.
Fallout: New Vegas