Question: why did ilya become reddington?
Answer: 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. A year later, Ilya was called by Katarina Rostova´s father Dominic Wilkinson to a meeting at a cafe in Belgrade.