Who developed a practical steam engine?

The first practical steam engine was developed by Thomas Newcomen and patented by him. It was developed around 1712 and described as an atmospheric engine. It was simply referred to as Newcomen engine.

It was considered the first steam engine to harness steam power and use it for mechanical purposes.

The Newcomen engine was so successful that it remained superior to all others for about fifty five years before it could be bettered.

The Newcomen engine was later improved by a man named James Watt who made it work more efficiently.