So, who invented the first steam engine and in what year? There are still at least four feasible answers. If you consider the aeolipile built by Hero in the first century A.D. to be a steam engine, because it made a ball rotate using steam power, even though it did no useful work, then Hero is the one who invented the steam engine.
If you consider it necessary that a steam engine does useful work, then Thomas Savery's 'fire engine' that was patented in 1698 to raise water out of coal mines could be considered to be the first steam engine. If a 'steam engine' must have moving parts and do useful work, then Thomas Newcomen, who built a more advanced 'fire engine' that operated with steam power to raise water from mines, would be considered the one who invented the steam engine.
Finally, Thomas Watt, who developed the steam engine so that it was capable of providing power to machinery in factories, in the latter quarter of the eighteenth century, is considered to be the one who invented the steam engine by some.
My vote is for Thomas Newcomen as the inventor of the steam engine in about 1712, because his 'steam engine' was the first with moving parts that did useful work.
For more contemporary steam engine information, check out Bright Hub articles about such topics as green steam engines and the use of steam on ships.