Hero is a solo campaign Achievement featured in Tom Clancy's Splinter Cell: Double Agent. It is unlocked by completing the game with the best ending (the ending that is canonical to the Splinter Cell series).
To get the Achievement, the player must meet some requirements before completing the last 'Undercover' level, JBA - HQ 4. The player must have NSA trust to be over 33%, and two of the three major choices in the game (jamming the Cozumel Cruise Ship bomb, sparing Hisham Hamza or sparing Irving Lambert) have to benefit the NSA side. Once these conditions are met, the player will get the bonus mission; completing this mission will unlock the Achievement.