It wasn’t any single entity–North Korea built their nuclear program through determination and theft.

They began research in the 1950s–The Soviets trained their scientists and built their first reactor.
After the Cold War, they stood alone–They were hungry, determined. In the 1990s, they found help–Pakistan’s A.Q. Khan sold them centrifuge designs.
They bought them with cash and missiles–Designs were uranium enrichment technology. Khan confessed this in 2004.

The North Koreans worked hard–They stole, smuggled, built their program piece by piece–through sanctions and poverty, they kept working.
China couldn’t stop them–America couldn’t stop them, the UN couldn’t stop them.
They tested their first bomb in 2006–It was small but real, they kept testing, bombs got bigger, carried more heft.
They made their own missile program too.

Now they have nuclear bombs and the missiles to carry them–But no one gave them a complete weapon–They built it themselves with stolen parts and borrowed knowledge.