Khizr Khan zoomed down the freeway headed to his northern Virginia home, praying the military chaplains who had called him at work were mistaken.

“Mr. Khan,” the chaplains had said on the phone that day in the summer of 2004. “We want to tell you that your son, Capt. Humayun Khan, was killed in Iraq.”

They must be wrong, he thought. Humayun S.M. Khan, 27, was a careful and deliberate young man. Khan couldn’t comprehend it — his son would not leave his family or his fellow soldiers like this. He drove in stunned silence to his home, where the chaplains sat waiting with his wife.

More than a decade later, Khan hasn’t gotten over the loss. But Thursday evening he will have the opportunity to share the story of his son — a Muslim American who died serving his country — during a prime-time speech at the Democratic National Convention. He will also stand as a symbol of the stark difference between the two major-party candidates running for president.

In inviting Khan, the Democrats appear to be showing a vivid example — the father of a Muslim American war hero — against Donald Trump’s characterization of Muslims, which indicates to many that they’d be treated as second-class citizens under a Trump presidency.

“This is our country too,” Khan, 65, said in an interview. “This is not only Donald Trump’s country. He is an ignorant, divisive manipulator, and through my message I wish to convey to him and to all Muslim Americans: This is our country too.”

Contrast with Trump

Khan’s speech comes months after Trump said he wanted a complete ban on Muslims entering the United States. In recent days, Trump has said he’d widen the ban and has shifted the focus to geography, saying he’d target visitors from certain parts of the world.

“People don’t want me to say Muslim. I prefer not saying it, frankly, myself. So we’re talking about territories,” Trump said in an interview on Fox News Channel Monday.

Khan, who now lives in Charlottesville, Va., and works as a legal consultant, was born in Pakistan. In 1980, the Khan family moved from the United Arab Emirates to Boston, where Khizr Khan attended a master’s program in law at Harvard University.

The family then moved to Maryland, where Humayun Khan went to high school before attending the University of Virginia and enrolling in the ROTC program. Humayun, described as an affable and driven young man, graduated with a degree in psychology and later joined the Army and was deployed to Iraq.

He quickly climbed the ranks to captain. He served as a counselor to soldiers and planned to attend law school following his military service and become an advocate for veterans.

On Mother’s Day in 2004, Humayun called home. His mom, Ghazala Kahn, doing what mother’s do, told him to be safe and to avoid trying to be a hero in a war zone.

“He said, ‘Mother, I promise I will be safe. I promise no harm will come my way, but I have a responsibility to my soldiers and I cannot leave them unattended,’” Khizr Khan recalled.

Weeks later, on June 8 at around 8 a.m., Humayun Khan and other soldiers were inspecting the front gates of their camp in Baquba, Iraq, when he noticed a speeding car blazing toward them. As soon as he saw the vehicle, Humayun ordered the soldiers to hit the ground. Local Iraqis waiting outside the gate also dropped.

As the car sped toward him, he took 10 steps toward it and kept his right hand in front of him signaling for the car to stop, his father said. The car, loaded with more than 200 pounds of explosives, blew up.

“Capt. Khan was killed, but his unit was saved by his courageous act,” Hillary Clinton explained in a December campaign speech nearly two weeks after Trump announced his Muslim ban. “Capt. Khan was posthumously awarded the Bronze Star and Purple Heart.”

‘We are Americans’

“It’s time to stand up and say: We are Americans,” she continued. “We will not turn on each other or turn on our principles. That’s what we do here. That’s who we are. That’s how we will win.”

The pain of his son’s death is still with Khizr Khan. Officials have told him that his son’s actions helped save the lives of hundreds of American soldiers.

“I still have not been able to put my arms around the sadness and the loss after all these years. Those words still ring in my ears. I wish I would not have heard them,” he said.

More than 12 years later, Khan is preparing to speak in a high-profile time slot Thursday night — just before Chelsea Clinton introduces her mother as the Democratic nominee.

Khan is admittedly nervous and has been practicing the speech repeatedly, but knowing that his son’s spirit will be with him on the stage gives him confidence. He will not be using the teleprompter but will instead speak from the heart.

“I am honored and humbled,” he said. “Nowhere but in the United States is it possible that an immigrant who came to the country empty-handed only a few years ago gets to stand in front of patriots and in front of a major political party. ... It is my small share to show the world, by standing there, the goodness of America.”

As for what he’ll speak about on stage, Khan will have a simple message to the American people: “Together we can solve the problems, and the solution is in joining hands, not building walls. Together we are stronger. The leader for us to move forward is Hillary Clinton.”

Hamed Aleaziz is a San Francisco Chronicle staff writer. Email: haleaziz@sfchronicle.com Twitter: @haleaziz