Step 1: Understanding the Concept:
The question asks to identify the historical figure credited with the first observation of microorganisms.
Step 2: Detailed Explanation:
Let's look at the contributions of each scientist:
\[\begin{array}{rl} \bullet & \text{1. Antonie van Leeuwenhoek (1632-1723): A Dutch cloth merchant, he is known as the "Father of Microbiology." He crafted high-quality single-lens microscopes and was the first person to observe and meticulously describe single-celled organisms, which he called "animalcules" (now known as microorganisms), from samples like pond water and tooth scrapings. } \\ \bullet & \text{2. Zaccharias Janssen (c. 1585-1632): He was a Dutch spectacle-maker who is often credited, along with his father Hans, with inventing the first compound microscope around 1590. However, he is not known for using it to observe microorganisms. } \\ \bullet & \text{3. Robert Hooke (1635-1703): An English scientist who, in his book *Micrographia* (1665), coined the term "cell" after observing the structure of cork under a compound microscope. He observed the cell walls of dead plant cells, not living microorganisms. } \\ \bullet & \text{4. Robert Brown (1773-1858): A Scottish botanist who discovered and named the cell nucleus in orchids in 1831. He also described Brownian motion. } \\ \end{array}\]
Therefore, Antonie van Leeuwenhoek was the first to see and describe living microorganisms.
Step 3: Final Answer:
Antonie van Leeuwenhoek was the microbiologist who first used a simple microscope to see tiny living organisms in pond water.