Atomic theory means the theory of the nature of matter or all small, hard, indivisible minute particles which may be of either the same or different kinds in their size, weight, and all other properties.
However, the ancient Atomic theory was proposed in Century only. Later many scientists gave their interpretations of the Atomic theory.
Thus, the Modern Atomic Theory was given by John Dalton (1766-1844) describing the nature of matter and giving some postulates.
The two laws were the basis of Dalton's Atomic theory which is (a) Law of conservation of mass and (b) Law of constant proportion.