Emperor Ling Tian
An OP elder is killed by his disciples and reincarnates with one goal in mind. To kill anyone in his way or so I suppose.
A great elder is killed by his disciples only to reincarnate in another body as Jiang Chen, who is considered to be helpless in cultivation. Through this reincarnation, he gains great knowledge of his past life and changes the course of his life for the better, gradually setting out to take his revenge against his disciples