Otto Warmbier used to have loud, enthusiastic conversations about economic theory in the hallway of his Ohio high school with one of his teachers. In his high-school yearbook, there’s a photo of him with the business club he co-founded: Everyone is holding up a dollar bill, and he and another student are lying on the floor in front of the group. He has a dollar bill in his teeth.

He’s “buoyant,” a longtime friend said immediately when asked about him. Warmbier wasn’t the class clown – he was way too earnest about academics for that – but he had a goofy, funny side. He seemed infused with happiness, one of those people who never let it show if he had a bad day.

“Always bright and energetic and positive, very passionate about school and very hard-working,” a friend said. “He felt unstoppable.”

Warmbier, a 21-year-old University of Virginia student honored as an “intellectual risk-taker,” was arrested in North Korea on Jan. 2 at Pyongyang airport as he prepared to leave after a five-day trip; the arrest was first announced Friday, when the official Korean Central News Agency said it was questioning him about taking part in “anti-state activity.” There was no indication of the allegations against him other than that he was “perpetrating a hostile act” against the country.

Details of Warmbier’s tour to North Korea were not immediately clear, but those who know him from U-Va. and from his childhood in Cincinnati described him as a kind-hearted, driven student.

Friends interviewed Friday agreed to speak on condition of anonymity because Warmbier’s family has told them they have security concerns related to his detention, but they unanimously praised him.

A longtime friend of the family described Warmbier in an email as “exceptionally smart” and “atypically mature, sane, polite, and reasonable. He’s a top notch person. … I have known Otto all of his life, and have never known him to make an unwise decision.”

Warmbier is the oldest of three children in a close, loving family, friends said. The parents are business people, very hard-working but supportive of their children — the type who would be cheering from the sidelines at every swim meet, a friend said. His father founded a firm based in Cincinnati, Finishing Technology.

A big guy, tall, a runner, a high-school soccer player and swimmer, friends said he is loud – a big presence, but never an intimidating one. He’s just happy, a friend said, very popular in a welcoming way, always ready with a grin and kind words.

He was always the one cracking jokes while they were warming up for soccer, a former teammate said, “always goofy, always a light-hearted smile. He’s the sharpest kid, with his head on straight.”

And he’s always been a driven student; he used to do all of his homework as soon as he got home from school on Fridays, a friend said.

He was a top student at Wyoming High School, a small well-regarded public school in an affluent part of Cincinnati. He was chosen to be Homecoming King by his classmates in 2012, and was one of three commencement speakers when he graduated in 2013, an honor given based on academic performance and character. A spokesperson for Wyoming City Schools did not immediately respond to requests for comment Friday.

“He’s a leader,” a friend said. “You feel you can trust him. You can follow him. He likes people.”

After graduation, Warmbier went to the University of Virginia, where he rose in the academic and social ranks at the elite public school. Now a third-year commerce student majoring in economics with a minor in environmental sustainability, he also is an Echols scholar, “intellectual risk-takers” chosen by the office of admission at U-Va. for their “academic excellence, intellectual leadership, and evidence of the ability to grapple with complex topics,” according to the school’s website.

A spokesman for the University of Virginia said only that they are in touch with Warmbier’s family and would have no further comment at this time.

Abraham Axler, president of the U-Va. student council, described Warmbier, a fellow student council member, as a well-admired junior on campus.

“Our thoughts are with Otto Warmbier and his family and we are certainly eager to have him return to the University,” Axler said. “He’s a vivacious, kind and involved member of our community.”

Warmbier advocated for environmental changes on campus, such as hand dryers in bathrooms, and helped manage the $20,000 portfolio for the Alternative Investment Fund, a finance group, according to his profile on Linkedin; rap music, vintage clothes and travel were listed as interests.

He’s a member of the Theta Chi fraternity. Leaders of the U-Va. chapter did not immediately respond to requests for comment, nor did officials with the fraternity’s national office.

On social media, Warmbier posted events such as an information session for U-Va.’s Alternative Investment Fund, a fundraiser for mental health at U-Va. in honor of a member of his fraternity who died last year, and a link to literary quotes. “All of these apply. So sentimental.”

“He’s inspiring,” a longtime friend of the family said. “I just don’t think he would ever consider that anything bad would ever happen to him. I don’t think it would enter his consciousness.”

An acquaintance of Warmbier described him as gregarious and fun, social and bright, and asked that people not jump to conclusions about the situation.