Christopher Poole, who was 15 years old when he created 4chan in his New York City bedroom in 2003, said that Hiroyuki Nishimura has taken his place as the owner.
Financial details of the acquisition were not disclosed.
"Hiroyuki is a pioneer in the world of anonymous communities, and can be thought of as the great-grandfather of 4chan," Poole said in an online post.
"None of us would be using 4chan today - or potentially any anonymous image board - if it weren't for him."
Poole, who uses the name "moot" for online posts, created 4chan as an online venue for sharing and anonymously discussing Japanese comics and anime.
The anonymous nature of 4chan has caused it to be a source of controversy as well as of "memes" that have gone mainstream, such as "Rickrolling" and "LOLcats."
Nishimura created 2channel in 1999 and inspired an "era of anonymous-centric web culture" in Japan, according to Poole, who said that the two became friends in 2011.
"He is one of few individuals with a deep understanding of what it means to provide a digital home for tens of millions of people for more than a decade," Poole said.
Nishimura sold 2channel six years ago.
The take-over came as 4chan was poised to pass the two-billion post milestone and celebrate turning 12 years old this month.
4chan boasts of being among the world's largest online forums, serving up some 680 million page views to more than 22 million monthly.
4chan is known to drawn a young audience, and about half of the users of the English language boards for sharing text, pictures or video are in the United States.