Mahabharata was written by Lord Ganesh but the authorship of the Mahabharata is attributed to Vyasa who with the help of Lord Ganesh has completed it.
It is known as the longest known epic poem and also been been described as "the longest poem ever written". Its longest version consists of over 100,000 shloka or over 200,000 individual verse lines and 1.8 million words in total.
Mahabharta describes the Kurukshetra War between Kaurava and the Pandava princes but it is more famous for Geeta a message of Karma which was passed by lord Krishna to Arjuna.