Branding giant Alan Siegel, who created the NBA's iconic logo, is leaving the Siegel+Gale firm that he founded 43 years ago.

Thursday or Friday will probably be his last day, a company spokeswoman told The Huffington Post on Thursday. Siegel, 74, was not available for an interview.

The NBA's silhouette logo of a dribbling Jerry West has generated billions of dollars in merchandising for the league -- and it has Siegel to thank for it. At a previous job in the late 1960s, Siegel had just finished overseeing Major League Baseball's centennial design -- a red and blue background framing the white silhouette of a batter, according to the Los Angeles Times.

Siegel then started his firm with Robert Gale in 1969 and went to work on the NBA's logo. While looking through archives of Sport Magazine, he spotted a photo of West, the Lakers' future Hall of Famer, dribbling with his left hand. Siegel became enamored with the image, he told the LA Times in 2010.

Then-NBA Commissioner J. Walter Kennedy wanted the logo to have an All-American vibe to rejuvenate the league's image, so Kennedy ultimately chose a red, white and blue color arrangement similar to baseball's.

Siegel and Gale devised the logo in about an hour, Siegel said in a video posted on YouTube (see below). The logo has endured since, but the NBA hasn't acknowledged that West is the dribbling player.

"They want to institutionalize it rather than individualize it," Siegel said in the LA Times story. "It's become such a ubiquitous, classic symbol and focal point of their identity and their licensing program that they don't necessarily want to identify it with one player."

HuffPost left a message with the NBA that wasn't immediately returned.

Siegel is also credited with getting banks, insurers and other institutions to use plain English on documents, including the IRS's 1040EZ form. He ran his company on the motto "simple is smart," according to a press release issued Thursday. "Simple" is also the name of his forthcoming book, to be published by Hachette Book Group's Twelve division.

“Alan is a key member of a very small group that helped shape the branding discipline as we know it today, and in the process built one of the world’s foremost brand experience and design consultancies,” co-company CEO Howard Belk said in the release. “Alan’s profound influence extends to many industries, the nonprofit world and the arts community. He will continue to have a recognizable impact on any organization or project in which he is involved.”

Siegel isn't fully retiring. An occasional blogger for The Huffington Post, he will also continue to teach and conduct research while serving as Siegel + Gale's chairman emeritus.