Kreza was killed earlier this month when his bike was struck by a driver suspected of being under the influence in Mission Viejo. Kreza had been training for a triathlon.
MORE: Costa Mesa fire captain dies 2 days after being struck by DUI suspect while cycling
The beloved fire captain's friends, family and community members gathered to remember his life at the Saddleback Church in Lake Forest.
Kreza's wife wrote a letter dedicated to her late husband. A loved one read the heartbreaking letter at the ceremony.
"When I lost you, I lost my everything. You were my rock, my protector and my very best friend...This gaping hole in my heart was once filled by the most loving, selfless human being I've ever known," Kreza's wife wrote.
Kreza's three daughters also wrote letters to their father. Letters written by Kaylie, 11, and Audrey, 7, were read for them on their behalf.
"Daddy I love you so much. All I know is that you will be with me in my heart every day and everywhere," Kaylie wrote.
"I will miss falling asleep with you on the couch. I loved watching you do your races. Daddy, you're the best daddy in the entire world," Audrey wrote.
His 9-year-old daughter Layla came up on stage and read her own letter.
"Dear daddy, I love you and miss you. You were the heart of our family. You're kind, loving, strong and fierce and the most important thing was that you were brave. I miss you so much and I always want to make you smile. You were the best daddy ever," she said.
Kreza's aunt recalled the first day she ever met him - on Jan. 31, 1974 at Hoag Hospital when he was born. She joked that at nearly 11 pounds, he seemed so large compared to the smaller babies next to him in the baby viewing room.
"He was so large. Mike came into this world large. He lived large, and he loved large. And became a large influence in so many that knew him," she said as she cried.
Fire engineer Steve Cathey called Kreza his best friend as well as his boss.
"I wanted to have the perfect speech because Mike was the perfect guy...Mike had a special bond with everybody that he touched...He put everybody ahead of himself," Cathey said.
Kreza was an 18-year veteran of the fire department. Firefighters presented a flag and Kreza's helmet to his grieving family.
"I can only pray that I will make you proud," his wife's letter read. "I will live every day for your legacy and for our girls."
A GoFundMe account has been set up to help his family with expenses.
The suspected DUI driver, 25-year-old Stephen Taylor Scarpa, has been charged with a felony count of murder. He faces 15 years to life in state prison if convicted as charged.