What is Reddington’s secret?
Liz's Father Is The Real Raymond Reddington The Blacklist season 6 seemingly revealed the truth, revealing that yes, Raymond Reddington IS Liz's father — but the man Liz knows isn't Reddington.
However, this isn't the first theory to suggest Red was actually Katarina Rostova (Lotte Verbeek), who was also Liz's estranged mother. One of the other major clues was from season one when Red first turned himself into the police despite being wanted as number one on the FBI's Ten Most Wanted Fugitives.
Ilya Koslov
In “Sutton Ross”, it is revealed that he is not Raymond Reddington but an imposter who has been using his identity for more than 30 years. In “Rassvet”, it is revealed that he is Ilya Koslov, a childhood friend of Katarina Rostova, the love of his life and her occasional lover.
Ilya devised the plan to impersonate Raymond Reddington in order to gain access to the money the Cabal placed in his name to frame him for treason, so they could fund Katarina´s new life.