For many who’ve been through war, the battles continue long after the guns go silent.

Through the years, we’ve come to know a veteran who owed his life to his best friend.

Luis Carlos Montalvan and Tuesday, his Golden Retriever service dog, have been inseparable for the past eight years.

Before they met, Army Captain Montalvan did two tours in Iraq, earning a Purple Heart and two Bronze Stars. But he returned broken in body and spirit -- a severe case of Post Traumatic Stress Disorder left him terrified to leave home.

“Drinking heavily to deal with physical and psychological issues,” he explained.

That all changed when he and Tuesday became partners, as he later told David Letterman.

“He brightens my days and he calms my nights,” Montalvan said on the Letterman show.

In this Tuesday, June 28, 2011 photo, former U.S. Army Captain Luis Carlos Montalvan, left, calls back his service dog “Tuesday” as he speaks during a book signing for his book “Until Tuesday,” at a book store in Coral Gables, Fla. Wilfredo Lee, AP

In 2011, Montalvan co-authored the best-seller: “Until Tuesday: A Wounded Warrior and the Golden Retriever who Saved Him”

He explained the title on Smile TV.

“He enables me to live my life,” he said. “If that isn’t life saving I don’t know what is.”

Tuesday learned more than a hundred commands, and he improvised when Montalvan was showing signs of stress, often laying his head on Montalvan’s hands so that he couldn’t type anymore on his laptop.

They toured the country together preaching a message of hope for those struggling with PTSD. Montalvan was also working on a second book.

But last week in El Paso, at just 43 years of age, Montalvan was found dead in his hotel room. People close him say they were stunned to learn he had left Tuesday with someone else for safekeeping.

The cause of death has not yet been determined.

But one thing is for sure -- nobody will miss him more than his best friend -- Tuesday.