As of today, David Karp is one of the richest, 20-something entrepreneurs in America.
But his dad says the sudden wealth—his 26-year-old son stands to make more than $200 million on the sale of the blogging website to Yahoo, announced on Monday—won't change David's work or outlook on life.
"He's going to keep on doing what he's doing," said Michael Karp, a New York-based composer of TV and film music themes. "It's never about the money with David. It's always been about doing what he loves doing. And creativity and passion."
He added that David is a very "thoughtful and down-to-earth guy" who won't let the money go to his head.
It remains to be seen how Tumblr and Karp will do under Yahoo's ownership. Michael Karp said he was with his son Monday morning at New York-based Tumblr when the announcement came, and David was "thrilled."
(Read More: Yahoo Agrees to Buy Tumblr)
He said David looks forward to continuing to run the company. "He's extremely passionate about what he does and about Tumblr," Michael Karp said. "He's going to focus on building the company. He loves the people he works with."
Karp said his son was a highly intelligent, focused child who became obsessed at an early age with computers. He said he bought him one of the early Apple computers. "This was before dial-up," Karp said. "David wanted to learn programming, HTML, everything."
David Karp grew up on Manhattan's Upper West Side. His mother taught science at The Calhoun School, which David attended until high school. He then went to Bronx Science but dropped out after a year to get home-schooled. "He wasn't happy there," Michael Karp said. "It wasn't a good fit. So we decided on home schooling. And that was before many people did home schooling."
(Read More: Tumblr Deal Gives Yahoo Social, Mobile Boost)
He said they hired tutors to teach David math, science and English and that David also took Japanese-language courses at the Japan Society. David's parents divorced when he was a teenager, though his dad moved a block away.
David lived briefly in Japan then returned to New York to form a web consulting business before founding Tumblr in 2007.
"I remember when he came up with the idea," Karp said. "He told me about it and was very excited. It was something he said he needed as a consumer but didn't exist. So he created it."
Although many reports say David founded Tumblr in his mom's apartment, Michael said his son also had an office provided by a family friend, animator Fred Seibert. In an interview with CNBC, David Karp said Seibert was an important mentor and "extraordinary human being."
"I met him because he was really eager to surround himself with more young people who kind of got the Internet, he could tell the Internet was going to be really important to this business and he wanted to surround himself with people who got it," Karp said. "That was my first big opportunity to sort of explore this space, explore this industry and my first opportunity to really code on a project, really write code for somebody else's big project. And it was this remarkable opportunity and it sort of threw me, not only into this industry, but also much more—mature is the wrong word—a much more focused environment."
When David was growing up, he had another role model: Steve Jobs. "He would watch all of Steve Jobs' speeches and talks on the Web," Michael Karp said. "He totally respected Jobs and his vision and what he did with Apple. Jobs was a very strong influence."
One thing he isn't likely to do, however, is move to the West Coast.
"He's a die-hard New Yorker," the father said. "He truly loves New York. I think he got that from me."
_ By CNBC's Robert Frank. Follow him on Twitter @robtfrank.
Disclosure: CNBC has a content-sharing partnership with Yahoo's finance site.