The concept of a particle theory of matter is ancient, with roots in ancient Greek philosophy. However, no single individual is credited with proposing it.

Here's a breakdown:

* Ancient Greeks: Philosophers like Democritus and Leucippus proposed that matter is made up of indivisible particles called "atoms". This was a philosophical idea, not a scientific theory.

* John Dalton: In the early 1800s, John Dalton formulated the Dalton's Atomic Theory, which provided the first scientific basis for the idea of atoms. He proposed that:

* Matter is made up of tiny, indivisible particles called atoms.

* Atoms of the same element are identical, but different from atoms of other elements.

* Chemical reactions involve the rearrangement of atoms, not their creation or destruction.

* Modern Atomic Theory: Dalton's theory was later refined and expanded upon by scientists like J.J. Thomson, Ernest Rutherford, and Niels Bohr, leading to the modern atomic theory, which describes the structure of atoms in terms of protons, neutrons, and electrons.

Therefore, while Democritus and Leucippus first conceived of the idea, John Dalton is considered the father of the modern atomic theory.