Samuel O'Reilly: The Inventor Who Revolutionized Tattooing

While tattooing has existed in various forms for millennia, the person most directly credited with making tattoos easier to put on human skin in the modern era is Samuel O'Reilly.

He patented the first electric tattoo machine in the United States in 1891. This machine was based on Thomas Edison's electric pen (originally intended for stencil making). O'Reilly adapted the rotary technology to drive a needle up and down, piercing the skin and depositing ink more efficiently and precisely than previous hand-poked methods.

Therefore, the answer is Samuel O'Reilly.