In interviews promoting his book, Kyle offered no regrets,
"I had to do it to protect the Marines," he told Time magazine a year ago. "You want to lose your own guys, or would you rather take one of them out?"
After his retirement from a decade's service in the Navy, Kyle became a businessman, a reality TV personalty, a supporter of fellow vets, an avid hunter and an outspoken opponent of gun control. He leaves behind a wife and two children.
His new ventures included joining other former SEALs in starting Craft International, a security company with the motto "Despite what your momma told you, violence does solve problems."
He also helped established the FITCO Cares foundation, a charity that helps U.S. war vets "who have survived combat but are still fighting to survive post-traumatic stress disorder," the group's website said.
Thousands pledged to toast him and Littlefield on Monday night, and hundreds expressed condolences on Kyle's Facebook fan page.
"Chris, thank you for your service; not only to the country you loved, but also to your fellow warriors that needed a helping hand," one woman wrote. "Rest in peace brave hero, patriot and warrior. You are missed."
The Facebook page also included a tribute to Littlefield, who the page's administrator wrote "felt deeply about the values of family, compassion, friendship and loyalty, and was equally as passionate about his love of God and country."
"Chad, thank you for your love for your country, the dedication to your country and your love for life," a woman said. "God has brought another angel home."