SEOUL, South Korea — Troy Collings, whose tour-guide company specialized in taking young budget travelers to forbidding places like North Korea, where one of his clients, the American Otto F. Warmbier, was imprisoned and fell into a coma, died last week, the company said on Friday. He was 33.

The cause was a heart attack, his company, Young Pioneer Tours, or YPT, said in a statement. No other details were provided. Mr. Collings, a New Zealander, was its managing director.

Mr. Collings’s company likes to say that it takes young travelers to “destinations your mother would rather you stay away from.” It is one of the few that specialize in taking tourists to North Korea, finding a marketing niche among young people who want to tour that secretive, totalitarian country at budget prices.

“Troy was instrumental in establishing Young Pioneer Tours as one of the leading travel companies for North Korea,” the YPT statement said.