Ethan Knox

Ethan Knox was a former employee of Lord Technologies.

Biography
Knox was an employee of Lord Technologies, but he got fired by Maxwell Lord however. His wife died shortly after, and his daughter became sick.

Terrorizing National City
On the behalf of his former boss, Knox planted a bomb on an old lab owned by Lord and did several other terrorist attacks on National City, in return for a lifelong doctor for his daughter. His two last attacks were that of National City Airport and Lord's new train. He planted the bomb at the airport and later went to the train, with an explosive jacket.

Death
He then explained to Supergirl that he was doing all the attacks for his daughter's life, and also said that his identity wasn't supposed to be revealed. He then said that she wouldn't save him, but would save the lives of the rest of the people on the train. She then separated Knox's wagon from the rest of the train. Knox's explosive jacket then blew up, killing him. In the end it was all a set-up by Maxwell Lord, Knox's identity wasn't supposed to be revealed but Lord knew that it was eventually going to be revealed. And consequently, Knox's intentions weren't suicidal. And finally, he was only used as a pawn to Lord.

Trivia

 * There have been several characters from other DC universes that had the surname "Knox", like Alexander Knox from the Batman (1989) movie and Ben "Bonk" Knox, a henchman of the Joker appearing in Batman Beyond: Return of the Joker and finally Curtis Knox from the TV Series Smallvile. None of these have actual relations to Ethan though.