Len Burman of the Tax Policy Center says it's James K. Galbraith:

Ezra Klein interviewed James Galbraith, who argued quite forcefully that “the danger [posed by the long-term deficit] is zero.  It’s not overstated.  It’s completely misstated.”
We now have an answer to the trivia question, “What do James Galbraith and Dick Cheney have in common?”  Cheney famously said, “Reagan proved deficits don’t matter.”
Cheney didn’t try to defend his argument.  He simply offered to take his critics hunting, which ended the discussion.
Galbraith, however, is absolutely convinced that he’s right and almost the entire economics profession is wrong. 
Galbraith is wrong.  To start, he doesn’t understand debt dynamics.  He says that when interest payments hit 20 percent of GDP, government borrowing will create inflation, which will make the debt go away.  He doesn’t account for the fact that a growing share of government spending is in the form of indexed benefits (Social Security, explicitly, and other entitlement programs like Medicare, implicitly).  Also, higher expected inflation translates directly into higher nominal interest rates, since lenders demand a hefty premium so their investment is not eroded by inflation.  The higher nominal interest rate applied to an enormous debt would cause nominal debt levels to explode.  Sudden inflation can devalue the debt, but only temporarily unless there are draconian cuts in real spending levels (to reduce deficits and convince financial markets that inflationary pressures will not persist).  And, of course, high inflation entails huge economic costs.