WASHINGTON — President Barack Obama’s emotional address on the Tucson, Ariz., tragedy was penned in part by a little-known 30-year-old Chicago native who works in the White House.

Cody S. Keenan, an alum of Northwestern and Harvard, worked anonymously for many months on what a friend called the “”eulogy and commencement beat.””

But he’s anonymous no more. On the flight back from Tucson, White House spokesman Robert Gibbs told reporters aboard Air Force One that Keenan had been the speechwriter.

“”It’s C-O-D-Y K-E-E-N-A-N,”” Gibbs said. “”And I’ll double-check that, but I’m almost positive.””

Gibbs added: “”A proud Northwestern fan.””

Keenan is the son of two now-retired ad execs. He cut his teeth working for Sen. Ted Kennedy of Massachusetts before joining Team Obama. It was Keenan who helped Obama write the eulogy when the Massachusetts senator died in 2009.

Gibbs, later Thursday, said the Tucson speech “”was very much the president’s”” and that ministers weighed in with thoughts and prayers and Obama reviewed Scriptures.

Keenan’s mother, an alum of the J. Walter Thompson advertising agency who now lives in Maryland, watched like millions of Americans. She said she and her son “”had talked about it for the last couple of days, every once in a while on the phone, so I had an idea where he was going.””

“”But it was more than I even expected and in my mind, it was exactly the right tone, what the president should be saying. I was really moved by it, as I think most people were, and I was very proud.””

Marilyn Keenan was on advertising teams credited with the old Corona Beer ad showing people frolicking on a beach with the exhortation: “”Change your whole latitude.””

She said her son, who was student body president in high school, had a talent with words early on. “”He’s always been a hard worker,”” she said. “”He was always a really good writer — always, always. He started reading at an incredibly young age.””

According to a Northwestern Magazine feature called “”Wildcats in the White House,”” Keenan earned a bachelor’s degree in political science at the university and later a master’s degree in public policy from Harvard’s Kennedy School of Government.

He was an intern and legislative assistant for Kennedy from 2004 to 2007 and became an intern with the Obama presidential campaign in 2007, the magazine said. He became a campaign speechwriter in 2008, it said.

Today he’s a $75,000-a-year presidential speechwriter, public records show.

According to Gibbs, Obama probably had his “”first conversations”” with Keenan late on Monday.

“”And what they usually do is the president will — they’ll bring a laptop in and the president will download a little bit on what he’d like to say.””

Obama sent edits back to Keenan about 1 a.m. EST Wednesday, Gibbs said, and work on the speech continued through the day. “”They made edits even after we landed in Arizona,”” he noted.

Asked if Obama felt good about the speech, Gibbs had two words: “”He did.””