Who was the first person to use animal testing?

There's no single person who can be credited as the "first" to use animal testing. The practice developed gradually over a long period. Early examples are difficult to document definitively, as systematic experimentation as we understand it today didn't exist. However, ancient texts hint at some rudimentary forms of animal experimentation, often related to observation and rudimentary surgery, rather than organized scientific testing. Therefore, pinning it down to one individual is impossible.