Here's the breakdown:
* Clyde Tombaugh meticulously compared photographic plates of the night sky taken weeks apart, looking for any objects that had moved. This was a painstaking process, and it was Tombaugh who ultimately identified the faint, moving object that we now know as Pluto.
* No one actually "saw" Pluto in the traditional sense until much later, when telescopes became powerful enough to resolve its tiny disk.
So, while Tombaugh was the scientist who first identified Pluto, he did so through careful analysis of photographic plates rather than directly observing it.