If you believe the United Nations' nuclear agency, Vyacheslav Danylenko is a weapons scientist who for six years used his knowledge of explosive detonators to help Iran move closer to its long-held, secret goal of developing a nuclear warhead.
If you believe Danylenko, he is a "computer dummy" who merely taught Iranian students how to create tiny synthetic diamonds for use in industrial grinding and polishing.
Danylenko, who was born in Russia but holds a Ukrainian passport, recently emerged as a key figure in the latest report
on Iran's clandestine nuclear program from the UN's International Atomic Energy Agency (IAEA).
He is, according to UN investigators and a prominent nonproliferation NGO, the "foreign expert" cited in the report whose lectures on explosion physics and its applications helped Iran develop a nuclear weapons detonator that was tested in 2003.
Danylenko(also spelled Danilenko) has not denied that his work at the Soviet-era Chelyabinsk-70 nuclear weapons facility was "highly classified" or that he lectured Iranian students on subjects related to explosive detonation.
But he told RFE/RL in a phone interview from Kyiv that the IAEA's description of him is "black PR."
"They have attached the label of a nuclear scientist to me, which I have never been. I understand absolutely nothing in nuclear physics," he said. "They also said that I created programs to model warheads. As any old man, I'm a computer dummy and I'm not familiar with any modeling programs. So there are tall tales that I'm a nuclear scientist and practically the founder of the Iranian [nuclear] program. It's just ridiculous."
LISTEN to the full conversation (in Russian):
Interview With Vyacheslav Danilenko
Danylenko's relationship with Iran began four years after the fall of the Soviet Union, in 1995, after a 30-year career at a secret Soviet nuclear weapons installation that specialized in making smaller versions of nuclear weapons.
There, he became an expert in creating high-precision detonators that could send a massive shock wave through a ball of weapons-grade uranium or plutonium, causing it to explode on cue.
The fact that the same type of blast, if directed at graphite, created a synthetic diamond that had industrial applications meant that Danylenko had a commercial skill after the Cold War ended and his services were no longer in demand by Moscow.
A new report
by the Washington-based Institute for Science and Security (ISIS) details how in 1995, Danylenko, who was searching for work, contacted the Iranian Embassy and offered to use his highly specialized skill in the country's production of nanodiamonds.
Danylenko said the Iranians "proposed that [he] write a series of lectures on the dynamic detonation synthesis of diamonds." He said he spent the next six years doing that, and nothing more.
"If I had had any connection to the [Iranian] nuclear program -- and I have strong doubts it existed at that time, most probably there was no such program -- if I had known any of Iran's top state secrets, I wouldn't have been allowed to leave Iran so freely. But I just said goodbye and left," he said.
But the IAEA's report says the agency confirmed, in multiple ways, that Danylenko's abilities were put to use in the development of a highly precise detonator that could trigger a nuclear warhead. Some of that information came from interviews with Danylenko himself, according to the report.
Evidence of his work was used to support the IAEA's conclusion that Iran has pursued the development of a nuclear weapon during the last decade.
Former UN nuclear inspector David Albright says it's "preposterous" to think that Danylenko was just some "ignorant guy helping on nanodiamonds." He says Danylenko's identity as a key player in Iran's nuclear weapons ambitions was an open secret among diplomats and experts close to the IAEA, which named him directly in its internal documents.
"I can understand why the IAEA decided to, in essence, name him in the report, because his story is not very credible. That's Danylenko's No. 1 problem: He hasn't convinced the IAEA that he didn't provide more information than he says he did," Albright says.
Danylenko's expertise in "shock compression" and his years of experience made him irresistible to the Iranians, says Albright, who now heads the ISIS. Judging by the person who replied to Danylenko's 1995 offer, he says, the Iranians knew just how valuable he was.
"He was contracted to do this work by a very senior Iranian who headed the Physics Research Center, which at that time was in charge of the entire secret nuclear sector, and so why would Dr. [Seyed Abbas] Shahmoradi bother to hire this guy to [make nanodiamonds]? It just doesn't hang together."
The IAEA's investigation turned up evidence of equipment bought by Shahmoradi for Danylenko to use in his work. It also discovered a connection that it said links Danylenko directly to the Iranian weapons program: a 2003 test of an instrument that measures shock waves as they impact a sphere. Danylenko co-authored a research paper describing the same instrument more than a decade earlier.
"So here you had a direct connection between one of his areas of expertise, which was diagnosing what happens when high explosives go off and an actual experiment done in Iran that's related to a nuclear weapon," he said, adding, "And he's refused to answer any questions about that, publicly."
Danylenko told RFE/RL that he was "waiting for all this to end" and doesn't want to speak to anyone further about it.
Staying silent might be his safest choice, for if he did use knowledge he picked up during his Soviet-era work to help Iran with its nuclear weapons program, Albright says he risks arrest.
"Russia has very tight security laws," he says. "If he admitted it, he could be in big trouble."