Acharya Kanad, an Indian philosopher, realized the theory of an indivisible particle while trying to break his food until he couldn’t any further. He called it ‘Parmanu’ - The fundamental particle.
His abstract theory leaned towards philosophy and logic than experimentation, it is praised even in the modern times as a brilliant and imaginative explanation of the physical structure of the world, and agrees with the discoveries of modern physics.
The atom. Realized.