John Dalton
John Dalton was born on September 6, 1766 in Eaglesfield Cumberland, England. He got his early education from his father and John Fletcher.
Now on to his atomic theory.
Dalton's atomic theory had four parts to it:
  1. All matter is made of atoms which are indestructible and indivisible.
  2. All atoms of an element are identical in mass and properties.
  3. Compounds are formed by a combination of two or more different types of atoms.
  4. Chemical reactions are a rearrangement of atoms.
A random marble
This is essentially Dalton's model for the atom; a solid sphere with no internal structure. Now just to be clear, he did get a couple of things wrong. First of all, not all atoms of a given element are identical in properties or mass, isotopes and ions ensure that. The other thing he got wrong was his model of the atom. We know today that it isn't solid but hey, at least he was trying.
Well, that sums up John Dalton's contributions to the world of the atom.