The concept of the constant acceleration for different objects due to gravity (at the same height and ignoring atmospheric effects) is usually attributed to Galileo. In reality, Galileo merely popularized the concept with his Tower of Pisa Thought Experiment (What happens if you drop a cannon ball and a musket ball from the top of the Tower of Pisa?).
John Dee (Elizabethan England) was well aware of the concept and did not think it particularly note-worthy - implying it was a well known concept amongst his peers.
So who was the first person to discover this non-intuitive concept?