RISHI KRIPACHARYA (Son of Shardwana and Janapadi) Kripacharya was the royal teacher of the Pandavas and Kauravas in Mahabharata. He was awarded immortality because of his impartial behaviour towards his students. He was declared as Mighty Maharathi by Bhishma who can fight 60,000 warriors simultaneously.
The hidden reason behind Kripacharya being immortal is his loyalty and his knowledge on how to train war techniques.
Secret scroll of Jwalaka: This book deals with light and speed and how to use it as a weapon.- Kripacharya