Ilya Koslov is a character on The Blacklist and an old friend of Raymond Reddington.
Background
Ilya Koslov is one of Raymond Reddington´s oldest and dearest friends and they seem to know each other since they were children. Not much is known about Frank´s past, however, there is the growing possibility that he is in fact Illya Koslov, the ex-KGB agent and Katarina Rostova´s former lover that supposedly became the current Raymond Reddington. The story that Dominic Wilkinson told Liz and Katarina Rostova about Illya is in fact true, but it was about the real Ilya Koslov and not Reddington.
Season 6
"Robert Diaz"
Season 7
"Norman Devane"
"Hannah Hayes"
"The Hawaladar"
"Orion Relocation Services"
It is revealed what happened in Belgrade.
"Katarina Rostova"
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