Constantine's original design was based on Sting from the Police.
Constantine first appeared in The Saga of Swamp Thing and was created by Alan Moore, Stephen R. Bissette, Rick Veitch, and John Totelben. The foul-mouthed warlock would prove to be popular as he would star in his own Hellblazer series, as well as becoming an integral member of both the Justice League Dark and occasionally, the Justice League. The character has been brought to live-action on multiple occasions, most famously portrayed by Keanu Reeves in the 2005 as well as on TV by Matt Ryan in his self-titled series and the CW's Legends of Tomorrow.
The story goes that Bissette and Totelben wanted to create a character who looked like Sting, as the pair were said to be fans of The Police. Characters designed like Sting even made their way into the background of issues of The Saga of Swamp Thing before Constantine was officially introduced in issue 37. Moore has cited Sting as the inspiration and even noted the character evolved into "something more than that now." Constantine's look is said to be inspired by Sting's look in the 1987 film Brimstone and Treacle. Ultimately, Constantine was a spitting image of Sting in the 80s: He had uncombed blonde hair, blue eyes, and wore a trench coat and tie, just like Sting's character from the horror movie.
Moore told Wizard Magazine (1993) that while Constantine's Sting-like appearance would slowly be phased out, it was definitely his intention to base the character's look on the singer.
But I can state categorically that the character only existed because Steve and John wanted to do a character that looked like Sting. Having been given that challenge, how could I fit Sting into Swamp Thing? I have an idea that most of the mystics in comics are generally older people, very austere, very proper, very middle class in a lot of ways. They are not at all functional on the street. It struck me that it might be interesting for once to do an almost blue-collar warlock. Somebody who was streetwise, working class, and from a different background than the standard run of comic book mystics. Constantine started to grow out of that.
Fortunately, Sting appeared to be totally thrilled with his looks serving as inspiration for Constantine. He ended up penning the introduction in the 30th anniversary of Hellblazer collection. It's pretty awesome to see that Sting didn't try to stop his inspiration in shaping Constantine's appearance, but has actively promoted and been enthusiastic about him over the years. It probably doesn't hurt that Constantine is among the most beloved antiheroes in comics who oozes cool every time he shows up - that's probably as good as it gets.