Would it be physicist Lord William Thomson Kelvin (1824-1907)? Did he not argue before the Royal Society of England that physics was nearing its end, and that there was nothing new to be discovered? Did he not also say that heavier-than-air flying machines were impossible? Is this the visionary scientist for whom a starship is named, in Abrams' Trek universe?
If you haven't already, I'd suggest reading "A Short History of Nearly Everything" by Bill Bryson. It's a fun book that often goes into interesting stories (but never anecdotes) about many MANY of history's greatest scientists over the centuries, many of whom declared that there was no more to learn in their respective fields, that they learned all that humanity could ever learn (you'd be surprised how often they'd say that). And that's not all; a few of them go out of their way to disprove things that are common knowledge today (ie the existence of atoms). And yes, even Einstein is in the collection. The funny thing is, a lot of the scientists who've said that are regarded today in the modern scientific world as heroes, such as Einstein and Kelvin.
