Many scientists contributed to the field of thermodynamics, so there isn't really one specific scientist who is credited with the whole theory and the laws. It was a collaborative effort beginning in the middle of the 17th century. The jumping off point was the invention of the vacuum pump by Otto von Guericke. Robert Boyle used Otto's design to build an air pump and create Boyle's Law, which shows that volume and pressure are inversely proportional to one another.
Another scientist, James Watt, worked with steam engines and added important information on heat capacity and latent heat to the field of thermodynamics. Building on all of the above information, scientist Sadi Carnot published a definitive guide and is generally considered to be the "father of thermodynamics."