Since ages, we've been told that according to Indian mythology's legends, lord Hanuman was immortal. That is the reason behind hisname "Chiranjeeva" which means the one who lives on earth forever .
But, there are six more prominent characters from our Indian mythology who were believed to be immortals.
One of them was Guru Dronacharya's son: Ashwatthama.
This tale begins with Dronacharya performing years of penance to please lord Shiva so he can be blessed by a son with a divinity like lord Shiva himself.
That was the birth of Ashwatthama, with a gem(mani) embedded on his forhead and with invulnerable powers. Now, as the epics narrated, Ashwatthama longed for revenge, to avenge his father's death as Pandavas deceived and killed his father, Drona. With unruly rage, Ashwatthama invokes the Brahmastra to kill arjuna, which he did not learn how to withdraw. This brahmastra gets directed towards Abhimanyu's wife uttara who was pregnant and destroys the life in the womb.
The raged Pandavas decide to kill Ashwatthama, but they get reminded of the blessing Ashwatthama has recieved from lord shiva, which was, to live forever.
As vengeance, Ashwatthama was asked to surrender the gem on his forehead. Lord Krishna then curses Ashwatthama to suffer immensly from all the agony till the end of mankind. His misery would be unbearable such that he would beg for death to take him away and provide an escape from the torment.
Fast forward to the current Era, few people in different regions of india believe that they have witnessed the presence of Ashwatthama. People believed that they saw a tall man(over 10 feet)in the forests near Lord Shiva's temples, as the legend says that Ashwatthama was a great worshipper of Lord Shiva.
A doctor in Madhyapradesh, claimed that he was treating a patient with a wound on his forehead and the bleeding from the wound wouldn’t stop despite of applying several medicines. The doctor also mentioned that the man disappeared on asking if he was Ashwatthama.
A lot of people claim to have seen him near himalayas.
A lot of folks who encountered a "strange man with a wound on his forehead" have shared their stories and experiences but the truth behind the existance of that "strange, tall man" is still a mystery.