Tasha Yar

Tasha Yar was former Helm Officer of the USS Enterprise before Worf was given the post. She was a brave officer with many varied skills, but unfortunatly she was killed early on in the Enterprise's career by a strange alien entity that looked like a blanket.

Yar was resurrected in a sense using a corrupted universe that was destroyed when the timelines of that universe co-incided with our own, allowing the alternate version of her to exist in our universe. However, she never met back up with the Enterprise, and instead (almost accidently) infiltrated the Romulan Empire, so in a sense she was able to live on almost in secret.