Silus

 is a member of Caesar's Legion captured during battle and brought to to Camp McCarran in 2281.

Background
Silus was an centurion in Ceasars Legion. But during an NCR attack which he lost he didn't commit suicide like normal legionares would, but decided he could escape captivity without revealing any information about Ceasars plans. The player can try to interrogate him at Camp McCarren during an unmarked side quest.

Interactions with the player character
Silus is held captive in Camp McCarran, and the NCR is attempting to interrogate him. He will not give information to the NCR, and interrogator Carrie Boyd is looking for help. She informs the player that the NCR does not allow torture of prisoners. The player can suggest a truth serum, beating the prisoner, or calling him names.

If the player has a high enough reputation with the NCR, Lieutenant Boyd will allow the player to go in and speak with the Centurion. The player will go in unarmed, unless the player's sneak skill is high enough to bring in holdout weapons. The player can speak with Silus or attack him outright. Should the player speak with Silus, a high enough speech skill will result in the legionary attacking. If your intelligence is at 8 then you can persuade him into thinking that you are working with the Legion and are here to assassinate him, this will result in him telling you all of his plans. After a brief fight, Lt. Boyd will come in again and ask Silus if he wants more. When the legionary refuses, the player will briefly speak to him again, and begin attacking once more. After a second round of fighting, Silus will talk, letting the player know that Caesar is sick and that there is a legionary posing as a member of the NCR at Camp McCarran.
 * Alternatively, through a series of either Speech or Intelligence checks, you can get him to reveal the same info without shedding any blood.

After the information is gained from Silus, you can no longer interact with him, and Lieutenant Boyd will pay you for your troubles.

If you leave the room after the first time you talk to Silus, you can not get back in, and further interaction with Lt. Boyd only result in her saying "Let's talk after we finish this up." and ending the conversation abruptly. There doesn't appear to be any way into the room at this point...

Also by talking to him you can break him out of the prison. You will not lose any rep. with the NCR because they won't know about it. Please someone elaborate on this about how to talk to him.

Appearances
appears in Fallout: New Vegas.