Caldwell and his cousin, whom friends say were like brothers, both lost their lives in the tragedy.
"I mean it was just a punch to the stomach. It was devastating," said family friend Adrienne Ciccone. "I mean he's 23 years old, newly married. . ."
Adrienne says Caldwell had just married his wife Claire in November.
She and Robert grew up together in Richboro, Bucks County. Adrienne said for as long as she can remember Caldwell wanted to be of service to others in a special way.
"He always wanted to be an elite firefighter. He wanted to be a firefighter, but it was never enough to just be a firefighter. He wanted to be a part of the brigades out there," she said.
Despite moving to Arizona some 15 years ago, Adrienne and her dad, Mark Ciccone, say Caldwell always remained a devoted Philadelphia sports fan.
"His dad just told me a really sad anecdote. The last day his dad saw him, which was two days before the fire, he had a 'Phillies Fan 'til I Die' shirt on," said Mark.
Sadder still is the fact that Caldwell and his cousin Grant McKee both lost their lives in that devastating wildfire. Friends here say they watched them grow up together.
"Found out that Grant perished in the fire, and then we were hoping that Robert was alive but then half an hour later we found out that both of them were gone," said Marie Teglas.
Robert Caldwell was a crew leader in the Granite Mountain Hotshots.
His parents now live in Prescott, Arizona. Friends say they are joining the families of the other 18 fallen firefighters, preparing to bury loved ones.