Complex sentence: In the latter, Isildur is revealed to be one of the Nazgûl before he was killed by the game's protagonist Talion who used his ring to prolong his life and became Isildur's replacement until his demise in the "Return of the King".
Split into simpler sentences: In the latter, Isildur is revealed to be one of the Nazgûl before he was killed by the game's protagonist, Talion. Talion take Isildur's ring to prolong his life and eventually became Isildur's replacement until the demise of the Nazgul in the "Return of the King".