The Identity Theft trophy in Borderlands 2 is story-related and can't be missed.
You will unlock the trophy once you complete the 14th story mission "The Man Who Would Be Jack".
*** Spoiler - click to reveal ***- Go to Opportunity
- Kill Jack's double
- Pick up double's pocketwatch
- Use info kiosk
- Get more voice samples: 0/4
- Retrieve voice modulator