Alan Gross spent 5 years in a Cuban cell. Tonight, he'll be at the State of the Union.

Alan Gross is an American aid worker who was imprisoned in Cuba for about five years on charges of undermining the Cuban government — and now he'll be at the State of the Union speech as one of First Lady Michelle Obama's guests. Gross' December release was secured as part of President Obama's historic deal aimed at eventually normalizing relations with the Cuban government.

Gross' time in prison was miserable: he lost about 100 pounds and, CNN reports, was also losing his teeth. His release is a humanitarian victory, and it's also an incredibly significant diplomatic move. His presence at the State of the Union is designed to highlight both.

Here's what you need to know about Gross — and why securing his freedom was so important for Obama's plan to improve American-Cuban relations.

Gross was sent by USAID to expand internet access for Cuban Jews

Gross, a 65-year-old non-Spanish speaker, was hired as a USAID subcontractor to go to Cuba in February 2009. His task was improving internet access for Cuba's Jewish community, which he did by installing wireless networks over the course of five trips to the island.

But there was a problem. The wireless networks installed could be used to bypass Cuba's internet surveillance regime. According to Stephen B. Kaplitt, the special assistant to the general counsel of USAID from 2004 to 2007, the aid agency should have known Cuba would perceive this as an attempt to undermine its government. In general, Cuba sees USAID activity as part of an American campaign aimed at weakening the Castro regime.

"Gross was never informed that his activities constituted espionage under Cuban law, nor did he have access to classified US intelligence assessments that might have pointed to the risk of imprisonment," Kaplitt writes in Politico Magazine.

Cuba arrested Gross, and it put Obama's plan to thaw US-Cuba relations on pause

Alan Gross takes a selfie with his wife, Judy Gross, while on board a US government plane headed back to America. (Lawrence Jackson/The White House/Getty Images)

At the end of Gross' fifth trip to Cuba in December 2009, the Cuban government arrested him. This was a major problem for US-Cuba relations —the US couldn't tolerate Cuban detention of a US worker and would need to secure Gross' release as part of any major deal, complicating negotiations.

When President Obama took office in 2009, he began relaxing sanctions on Cuba as part of a broader effort to engage the Cuban government. According to the Guardian, ongoing US talks on migration issues and expanding direct-mail service were suspended after Gross's detention, restarting only in 2013.

"The incident has soured the Obama administration's cautious outreach to Cuba," NPR's Nick Miroff wrote in 2010. "Gross' arrest is now a major obstacle to any US negotiations with Cuba."

With his freedom, that significant obstacle is gone, and it has opened the door to normal US-Cuba relations. The Alan Gross portion of this diplomatic saga appears, thankfully, to be over.

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