At a startup talkshow at the Hanoi University of Science and Technology on Monday, Dong, in a dark blue sweater, black jeans and light brown leather shoes, remained quiet and reserved and spent more time listening than talking.

The host of the event said at the introduction: "Dong is a humble person, living in a world of his own. Surrounding Dong is a veil of mystery. Dong isn't like [other] successful people; he doesn't like appearing in media, therefore Dong becomes even more intriguing."

But even when asked to unveil the mystery around himself, Dong did not talk much, and seemed hesitant about sharing his story.

He told the students: "For the past 17 years I have only had the computer screen; so there aren't many stories to tell. I think I had to trade off a number of things to achieve such success. The thing that I exchanged was my maturity."

Alluding to his decision to take down Flappy Bird when the app was at its peak in February 2014, Dong said he has been unable to handle pressure since birth, so taking it down was his best option.

Five years ago U.S. pop culture magazine Rolling Stone published an article on the success of Dong and Flappy Bird, the first time he had shared his story with the public.

It said: "By February [2014] it was topping the charts in more than 100 countries and had been downloaded more than 50 million times. Nguyen was earning an estimated $50,000 a day. Not even Mark Zuckerberg became rich so fast."

It was this success that made CNET name Flappy Bird among the 25 most impactful apps of the decade alongside others such as Instagram, Twitter and Facebook.

In the U.S., some would say a person could be considered financially successful and retire if they earn $1 million. Dong too, while in university, had similar thoughts.

"Back when I was a student, I calculated that once I had $1.1 million I would retire, but now I have multiple times that amount but I still cannot retire," he said.

Five years after taking down Flappy Bird, Dong now runs a gaming company with a friend, also a former student of the Hanoi University of Science and Technology.

After the smashing success of Flappy Bird, many are waiting for an encore from Dong, which he however thinks is unlikely.

"The probability of achieving similar success is 0.1 percent. I don't want to say beforehand because [that] will make it difficult to achieve."

He shared some information about his new game, claiming it "looks very simple but the level of technology in this game is unprecedented."