Just Do It, or JDI for short, is a trademark of shoe company Nike, and it is one of the core components of Nike's brand. The slogan was coined in 1988 at an advertising agency meeting. The founder of the Wieden+Kennedy agency, Dan Wieden, credits the inspiration for his "Just Do It" Nike slogan to Gary Gilmore’s last words: "Let's do it." The "Just Do It" campaign allowed Nike to further increase its share of the North American domestic sport-shoe business from 18% to 43%, (from $877 million to $9.2 billion in worldwide sales) from 1988 to 1998.

Source: Wikipedia