Nathaniel Hartford, also known as The Outcast, was the husband of Grace Cahill and the main antagonist of the Doublecross series. He was born in 1926. He is Hope Cahill's father, and Amy and Dan's grandfather.
Before he married Grace, it is said that he went to Harvard and was a poet. He supposedly died in Moscow in March of 1967, but it is revealed in Mission Hindenburg that Vladimir Spasky failed to kill him. Vladimir Spasky also tells Nellie that he has a thirst for revenge.
He is the Outcast that is shown in Mission Hindenburg. Hartford is still alive, and on the last few pages of Mission Hindenburg, it says that the Outcast wants the Ekat branch for himself, Vikram Kabra gets the Lucian branch, because all the leaders were killed.
According to Beatrice, even though Fiske disagrees, Grace made him an Outcast because he asked for divorce and then put out an kill order on him. As discovered in Misson Hindenburg, and proved in Mission Atomic, Nathaniel Hartford is discovered to be an Ekat. He caused the Chernobyl disaster to happen. At the end of Mission Atomic, he was killed by genetically modified bees.