Nelson is the security guard of Arkham Asylum.
Lex Luthor's Escape
While the inmates were leaving their cells with the security guards of Arkham Asylum, Nelson began calling Lex Luthor to leave his cell. He came out of his office, approached the cell and met an imposter, which means the real Lex Luthor escaped from Arkham. 
While Nelson called Luthor out of his cell, he warned him as he went to the cell and suspectedly found the wrong prisoner. When the guard found an imposter, he was shocked that Luthor escape from Arkham.
- Lex Luthor - Prisoner