Ol' Buddy Ol' Pal

Ol' Buddy Ol' Pal is an achievement and trophy $$

Requirements
It is awarded for successfully convincing one of the eight Fallout: New Vegas companions (ED-E, Craig Boone, Veronica, Lily Bowen, Rex, Arcade Gannon, Raul Tejada, or Cass) to join the Courier.

Bugs
This appears to only be triggered by the very first companion you recruit, so if achievements are disabled at that time, recruiting other companions later will not unlock it.