Phoenix police Sgt. Trent Crump said the man was the driver of a Toyota Corolla that was hit head-on by a minivan full of children.
He was identified as 31-year-old Matthew DeJarnett.
DeJarnett's brother, Jeffrey, said Matthew and his wife moved to the Valley less than a year ago from Oklahoma.
"He was a sweet guy, a big teddy bear, everybody loved him," said Jeffrey.
Jeffrey said his brother was on his way to school when he was hit head-on.
Matthew attended Carrington College and wanted to become a radiology technician.
Matthew was the middle child of three children.
The collision happened just after 7 a.m. Monday near Southern and 59th Avenues.
Crump said the unlicensed 16-year-old driver of a Dodge Caravan was driving his six siblings to their first day of school.
Crump said detectives evaluated the driver of the mini van, and signs of impairment were observed. Blood was obtained through a search warrant for testing.
However, friends of the teen driver came to his defense.
"That's my Godson. I've never known him to smoke weed or drink like that. It was early in the morning. What would a 16-year-old need a drink for that early in the morning? He's not a bad kid. He's into sports and all that too so I don't believe that," said LaTonya Stewart.
Witnesses told police the mini van was traveling at a high rate of speed westbound on Southern Avenue, according to Crump.
The driver then appeared to have made an unsafe passing movement to the right of other traffic, leaving the road where it narrowed to a single westbound lane, he said.
Crump said the driver then overcorrected while trying to get back on the road and lost control of the vehicle.
The mini van went left of center and crashed into the Toyota Corolla, which was traveling eastbound on Southern Avenue, said Crump.
Dejarnett was properly restrained and air bags deployed, but he later died at a local hospital, according to Crump.
No one in the mini van was properly restrained, Crump said. Several of the children were ejected from the vehicle.
One of the children was pronounced dead at the scene, and others were transported to nearby hospitals.
Two other children were pronounced dead later in the day.
The victims were identified as 4-year-old Dominic Johnson, 5-year-old Mikquan Johnson, and 11-year-old Jaymon Hamilton.
The driver and two passengers have "incapacitating injuries" and a 3-year-old girl remains in critical condition, Crump said.
At this point, Crump said it's too early to talk about charges. Investigators are still conducting interviews, waiting on reports from the medical examiner's office as well as the blood results taken from the teen driver.
Jeffrey said his brother's funeral will be on Monday in Oklahoma but said his family appreciates all of the support they've received from the Valley.