Night's Shadow was an ancient creeper that lived before Herobrine came. He was friends with Tiger's Roar for a long time and had a dark heart. He wished to be leader, even though he was already a deputy (rank below leaders).
Night's Shadow was littermate with Tiger's Roar and the were very close. After growing up, they desided they wanted to be leaders, even though Cloudy Night was already in the highest position. Along with Sun Claw and Gator's Rage, they attempted to take down Clooudy Night but failed.
Night's Shadow lived a long time, and became very good friends with Herobrine.