SLIDELL — Throngs of solemn mourners gathered at Slidell Municipal Auditorium for the funeral service of Sgt. Michael Guillory, saluting a native son who was killed Dec. 14 while on duty in Helmand Province, Afghanistan.

Guillory, 28, who was born in Slidell and grew up in Pearl River, was remembered Saturday as someone who tackled life with enthusiasm and considered serving his country a high honor.

Bart Walker, who served as the family’s pastor when Guillory was growing up and who officiated at the funeral service, said his memories are of Guillory as a child.

“Every time I saw him, he had a red Kool-Aid mustache, and he was always sweaty,’’ Walker said, explaining that, “whatever Michael did, he went 100 percent at it, whether it was dodgeball, kickball or football.

“I remember him so much as a child,’’ Walker said. “But he died as a man.’’

Guillory served nine years in the Marine Corps, beginning his service in March 2003 as a combat engineer, according to a U.S. Marine Corps Special Operations press release. He was assigned to the 1st Marine Special Operations Battalion, U.S. Marine Corps Forces Special Operations Command, which is based out of Camp Pendleton, Calif.

He was killed in a vehicle accident while supporting resupply operations as part of a village stability operation, according to a U.S. Marine Corps Special Operations Command press release.

He was taken to a nearby medical facility, but could not be resuscitated, the press release said.

The accident is still under investigation, said Maj. Jeffrey Landis, a MARSOC spokesman. He told the Marine Corps Times that an improvised explosive device was not the cause.

Clay Harper, who spoke at Guillory’s service, said his lifelong friendship with Guillory began in preschool and continued through Sixth Ward Junior High and Pearl River High School. Harper described Guillory as someone with “the biggest heart.’’

“He was not a follower, he was always a leader,’’ Harper said. Whatever he did, it was “with 100 percent commitment and a smile on his face,’’ and Guillory frequently dismissed his own achievements as “no big deal,’’ Harper recalled.

That included his success in the Marine Corps, which promoted Guillory to the rank of corporal while he served in Iraq.

Later in his career, he was selected to attend the Individual Training Course, graduating in July 2009 as a Critical Skills Operator. After receiving orders to 1st MSOB, he served as team member and later assistant element leader.

Guillory deployed in support of Operation Enduring Freedom as well as Operation Iraqi Freedom

Hundreds of people lined the streets of Slidell on Thursday, when Guillory’s body was driven back to St. Tammany Parish. His visitation and funeral service also were packed.

Before the funeral service began, a large screen flashed images of Guillory, many of the pictures depicting his life as a Marine.

Mourners who stood in line to file by his casket included those in uniform from various branches of the armed forces, including the Navy and Air Force.

Members of the Blue Star Mothers of Louisiana presented his parents, Gina and Michael John Guillory, with a gold star in recognition of their sacrifice. Guillory is also survived by two sisters, Tiffany Guillory, who is a gunnery sergeant in the Marine Corps, and Jessica Guillory.

Many Marines were on hand at the funeral, serving as pallbearers and rendering other military honors. At the conclusion of the service, a Marine Corps rifle team fired a crisp three-volley salute under a cloudless sky.

The Marine Corps was Guillory’s “passion and purpose in life,’’ Harper said. His friend “considered it an honor to serve our country and protect our freedom. You will always be a big deal to us,’’ he said.