What do you mean by this? What made him a DEI darling? What is a DEI darling?
Are you seeking a exhaustive, scientific definition of a casual term? I did not mean to confuse anyone, lol.
(I'm imagining someone reacting in a similar manner to a claim of having a "good sandwich" or seeing a "sexy woman".)
The reference is in relation to him having been invited by President Obama to the Whitehouse to engage with other officials on DEI issues, his work on inequality and race has been widely cited (before the paper that caused him so much trouble), and he has testified before congress on relevant matters to the DEI movement.
See, for a small example, his contribution "Valuing Diversity", published by Harvard in March 2013.
If you'd like more, or have a more specific question, I will oblige.
Take a sample from how the press treated him BEFORE the paper was released:
https://www.psu.edu/news/academics/story/alumnus-receives-major-prize-young-economists/
Or the type of presentations that helped him rise to fame:
(The above video is from his winning the Calvo-Armengol International Prize)
It's probably also worth mentioning he was NYC's Chief Equality Officer as well.
I'd argue you'd be hard-pressed to find many academics with equal, much less stronger, DEI related and relevant credentials anywhere.