It's difficult to say definitively who first used a microscope, as early magnifying devices predate documented use. However, the invention of the compound microscope is often attributed to Zacharias Janssen in the late 16th century.

Here's a breakdown:

* Early magnifying devices: While not technically microscopes, magnifying glasses were used for centuries before Janssen.

* Zacharias Janssen: Around 1590, he is credited with creating the first compound microscope, a device with two lenses that magnified objects further than single lenses. However, there's debate about his exact contributions, and some historians believe his father, Hans Janssen, was involved.

* Galileo Galilei: In 1609, Galileo independently created a compound microscope with a magnification of about 20x. He used it to study insects and other small objects.

* Cornelis Drebbel: Around 1620, Drebbel built a compound microscope that could magnify objects up to 150 times.

Therefore, while Zacharias Janssen is often considered the inventor of the compound microscope, it's important to acknowledge that others likely played a role in its development and early use.