Dan Wieden, co-founder of advertising agency Wieden+Kennedy and advertising executive of Nike, said in an interview with Dezeen that he came up with the slogan because he got inspired by Utah killer Gary Gilmore. Gilmore was sentenced to death in 1977 for robbing and murdering two men. Here is a sample of his interview with dezeen:
Marcus Fairs: You're probably bored to death of this question but tell me how the Nike slogan came about.
Dan Wieden: So, it was the first television campaign we'd done with some money behind, so we actually came up with five different 30 second spots. The night before I got a little concerned because there were five different teams working, so there wasn't an overlying sensibility to them all. Some were funny, some were solemn. So I thought you know, we need a tagline to pull this stuff together, which we didn't really believe in at the time but I just felt it was going to be too fragmented.
So I stayed up that night before and I think I wrote about four or five ideas. I narrowed it down to the last one, which was "Just do it". The reason I did that one was funny because I was recalling a man in Portland.
He grew up in Portland, and ran around doing criminal acts in the country, and was in Utah where he murdered a man and a woman, and was sent to jail and put before a firing squad. And they asked him if he had any final thoughts and he said: "Let's do it".
And for some reason I went: "Now damn. How do you do that? How do you ask for an ultimate challenge that you are probably going to lose, but you call it in?" So I thought, well, I didn't like "Let’s do it" so I just changed it to "Just do it".
I showed it to some of the folks in the agency before we went to present to Nike and they said "We don't need that shit". I went to Nike and [Nike co-founder] Phil Knight said, "We don't need that shit". I said "Just trust me on this one." So they trusted me and it went big pretty quickly.
Marcus Fairs: Most of Dezeen's audience is involved in making products, whether it's trainers or cars or whatever. What is the relationship between what you do and the product?
And so on...
So, the claim in question is true according to Dan Wieden.