The man named the "great successor" to take control of North Korea in the wake of the death of Kim Jong Il, is a baby-faced twenty-something with virtually no public profile outside of his home country.

Kim Jong Un, known only to be in his late 20s, has gained the little profile he has over the past three years -- as he has slowly been pushed forward as the man to take over from his ailing father.

On Monday, that transition was seemingly complete, with North Korean state media reporting that the younger Kim, born to the late leader's third wife, was the "great successor" to his father.

"Standing in the van of the Korean revolution at present is Kim Jong Un, great successor to the revolutionary cause of juche and outstanding leader of our party, army and people," the country's official news agency said, referring to the official ideology of juche or self-reliance, AFP reported.

"Kim Jong Un's leadership provides a sure guarantee for creditably carrying to completion the revolutionary cause of juche through generations, the cause started by Kim Il Sung and led by Kim Jong Il to victory."

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But it was only in September, 2010, that the first ever adult picture of Kim Jong Un was run by state media -- after he was appointed as a four-star general and given senior ruling party posts, The (London) Times reported.

The photo shows a young man, who looks not much older than a teenager, standing next to his father at a formal event clapping his hands.

More recently, North Korean media has started calling the younger Kim the "Little General," The Times reported.

US intelligence agencies have closely studied Kim Jong Un for nearly three years after word came out of Pyongyang that a political transition had begun, The Wall Street Journal reported.

But Washington has also privately voiced concerns that the younger Kim might not be able to consolidate power as his father did after taking power in 1994, potentially leading to greater instability.

In recent months, state media began referring to him as "general," after having previously only used his official title -- vice-chairman of the central military commission of the Workers' Party of Korea, AFP reported.

"The latest move indicates Kim Jong Un is being put forward formally as a powerful leader like his father," Sejong Institute analyst Cheong Seong-Chang, a specialist in the succession issue, said in October.

"Such a title has been used internally, but North Korea now appears to be boosting the image of Jong Un as military leader," he said.

Little is known about the succession. South Korea's top official on cross-border affairs said last month that there would be challenges in transferring power to the son.

Kim Jong Il's only sister Kim Kyong hui and her husband Jang Song thaek, the country's unofficial number two leader, are expected to act as his guardian and throw their political weight behind him, analysts say.

In a memoir, Kenji Fujimoto, a former Japanese sushi chef for Kim Jong Il, described the Swiss-educated Jong Un as a "chip off the old block, a spitting image of his father in terms of face, body shape and personality."

"Jong Un is known to have the potential to become a strong, ruthless leader. He has a take-charge personality," Sejong Institute's Cheong said.

Jong Un is believed to have studied at an international school in Switzerland under a false name. Newspaper reports say he enjoyed basketball and drawing cartoons in Switzerland, where school staff and friends reportedly remembered a shy boy who liked skiing and Hollywood tough guy Jean-Claude Van Damme.

Back in Pyongyang, South Korea's Yonhap news agency has reported, he attended the Kim Il Sung Military University and graduated in 2007.