In the Hindu epic poem the Mahabharata, Sanjaya is a trusted advisor to King Dhritarashtra. He is the ultimate war reporter.
During the Battle of Kurukshetra, Sanjaya goes to the battlefield as an observer and messenger for the King. He narrates the entire war to Dhritarashstra. Krishna gives extra perceptive abilities to Sanjaya so that he doesn't miss any of the action.
His descriptions for the blind king are intense and colorful. He is the person narrating the Bhagavad Gita- the famous philosophical conversation between Krishna and Arjuna, which takes place in Arjuna's war chariot just as the battle begins.
Sanjaya becomes King Dhritarashtra's charioteer as well, so he is not just functioning as his eyes -- he is also a spiritual guide.