Professor Merrit Erskine was a planetary surveyor who was tricked into surveying Death's Deal by the Wraith Mining Cartel who then shot him down. He survived and discovered the prescence of slaughter crystals and kept records on them. He had a wife and a daughter called Lyric whose pictures he kept in a locket around his neck.
When the Tenth Doctor and Donna Noble landed on Death's Deal they were instructed by the Eleventh Doctor to find him and gain his research on slaughter crystals. The Doctor found him and reunited him with his daughter. Merrit Erskine was later killed whilst trying to sacrifice the Doctor and Lyric to the planet. (AUDIO: Death's Deal)