From playing a don in 1978 movie Don to botany professor in Chupke Chupke, Amitabh successfully showed various shades on screen.
"An actor does don many (roles), professionally. But which the real is and which not, shall always remain a mystery, not just for those that observe him from the outside, but for the actor himself," Big B wrote on his blog.
"It is often asked of us, 'Who the real Mr Bachchan is?' and it is often replied with an inconclusive, incomplete and an utterly unconvincing response. Not because there is difficulty in finding an adequate reply, but that there really is none," he added.
However, the actor finds questions about his real self negative.
"The question itself is in many respects incongruous. There is a touch of insinuation in the asking, because the person seeking response, has determined beyond all reasonable doubt that there are more than one person behind that name. This is objectionable in a funny sort of way," he wrote.
The actor has wrapped up shooting for Prakash Jha's political drama Satyagraha and will soon be seen in Hollywood project The Great Gatsby, the opening film at the 66th Cannes International Film Festival.