Wow! I have no idea. For one thing, you have to decide when you could really call someone a scientist. Can we call the Greek philosophers scientists or do we have to wait until the middle ages or later? Even so, there were many, many inventions in our early history (the wheel, agriculture, alphabet, money, paper...) that we all take for granted but weren't necessarily developed by "scientists."

It depends on whom you call a scientist, but the early humans who discovered that certain flint stones could be broken in such a way that the edges were sharp and could be used as knives and arrowheads could be considered early scientists and inventors. This would be many thousands of years ago during the Stone Age.

A scientist is somebody who uses the scientific method, which, instinctually, we all are at birth, although too many of us forget our instincts. I would postulate that we have had this instinct for as long as we have had the capacity to learn for our benefit. This was well before the origin of humanity, and many animals in the modern world use tools, from other apes, seals, even octopus. Chimpanzees at least actually make tools; I do not know how ubiquitous this is among other animals, but I would be surprised if this is limited to just humans and chimps. So what was the first tool? The ancestors of the octopus and squid likely possessed their intelligence hundreds of millions of years ago, before the dinosaurs.