Isaiah Hartenstein poses for a photo with his parents Theresa and Florian Hartenstein in June 2025.
Isaiah Hartenstein poses for a photo with his parents Theresa and Florian Hartenstein in June 2025.
Oklahoma City Thunder center Isaiah Hartenstein was born to his parents, Florian and Theresa Hartenstein, in 1998
Isaiah grew up watching his father play professional basketball in Germany
Now, Florian and Theresa are grandparents to their daughter's child and Isaiah's son
Isaiah Hartenstein's parents laid the foundation for his basketball career long before he ever stepped onto an NBA court.
The Oklahoma City Thunder center was born to Florian and Theresa Hartenstein in Eugene, Ore., in 1998. However, Isaiah spent much of his childhood in Germany, where his father played professionally and later coached.
Basketball wasn’t just a sport in the Hartenstein household; it was a way of life. “We had a basketball carpet in the house. We had a basketball hoop, all that kind of stuff,” Florian told Bleacher Report in 2017.
He continued, “[Basketball] was always part of it. And then once he came over to Germany, again he was in the gym all the time. I had the chance to coach him after that a little bit. And so, we were a basketball family. He never really had a chance to not play."
Theresa added that her son’s passion for the game started early and never wavered. “Since he was a baby, he never had stuffed animals; he always had a ball,” she said.
From their early days in Oregon to supporting their son in the pros, here’s everything to know about Isaiah Hartenstein’s parents, Florian and Theresa Hartenstein.
They met when Florian was in high school and Theresa was in college
Isaiah Hartenstein with his dad Florian Hartenstein.Isaiah Hartenstein with his dad Florian Hartenstein.
Isaiah Hartenstein with his dad Florian Hartenstein.
Theresa and Florian met while she was a student at the University of Oregon and Florian was still in high school, they told Bleacher Report. The two eventually married and welcomed Isaiah in 1998 at Sacred Heart Medical Center in Eugene.
Florian was ultimately signed to a basketball team in Germany and lived abroad while his family continued residing in Oregon. However, when Isaiah was 11, he and his sister and mom joined Florian in Germany in an effort to keep the family together.
"For some people that play overseas, it works for [the family] to stay in the States and the husband to be overseas. But our family is so close, it was so hard for the kids," Theresa told Bleacher Report. "I thought anything that we can do here, we can give up. But we can't rewind the clock as they are growing up to keep that bond."
Florian was a professional basketball player
Martynas Mazeika of Bonn is blocked by Florian Hartenstein of Giessen during the Bundesliga game between Telekom Baskets Bonn and Giessen 46ers on October 14, 2006 in Bonn, Germany.
Martynas Mazeika of Bonn is blocked by Florian Hartenstein of Giessen during the Bundesliga game between Telekom Baskets Bonn and Giessen 46ers on October 14, 2006 in Bonn, Germany.
After playing college basketball at the University of Oregon, Florian went on to have a professional career in Germany, signing with the Gießen 46ers. He later played for the Artland Dragons in the town Quakenbrück, where he eventually transitioned into coaching and even coached his son.
Florian believed that playing in Europe, as opposed to the NCAA, gave Isaiah a more well-rounded foundation for the NBA, especially as the role of taller men evolved.
“Right now is a time where most big guys have to be able to play from the outside,” Florian told Bleacher Report. “That was one of the goals. We had a feeling that if he were to go to college, he would just clean up around the basket, just because he's 7 feet tall."
He continued, "And in Europe, he has more of a chance — the coaches believe he can also play from the outside. So, I think for his development and the style of basketball he plays, European basketball was better.”
Theresa was a dance coach
Isaiah Hartenstein's mom Theresa Hartenstein with her dog in May 2021.
Isaiah Hartenstein's mom Theresa Hartenstein with her dog in May 2021.
Theresa brought her expertise in dance and cheerleading to Quakenbrück in 2009, quickly becoming a driving force behind the local cheer community.
As the coach of the Flames Dancers, the spirit squad for the Artland Dragons, she played a pivotal role in elevating the team’s performance and professionalism. She also coached her daughter Jasmine before leaving in 2020.
“Thank you all so very much I am so very proud of all of you and all of the Flames and stunters I have had the amazing opportunity to coach,” Theresa wrote in the comments section of a sweet post by the team on Instagram wishing her well as she ended her coaching tenure.
They have two children
Isaiah Hartenstein and his sister Jasmine Hartenstein in February 2017.
Isaiah Hartenstein and his sister Jasmine Hartenstein in February 2017.
Isaiah's older sister Jasmine was born in 1992, making her six years older than him. Following in her mom's footsteps, Jasmine has carved out her path in the world of dance, working as a choreographer, cheerleader and performer.
For years, she was a member of the Flames Dancers. In 2022, Jasmine joined her family in relocating to the United States where she continued to pursue her choreographing career.
They are grandparents
Isaiah Hartenstein smiles with his family in July 2024.Isaiah Hartenstein smiles with his family in July 2024.
Isaiah Hartenstein smiles with his family in July 2024.
Florian and Theresa aren’t just proud parents; they’re proud grandparents, too. Jasmine welcomed her son, Shawn Michael, on Jan. 17, 2016, and Florian has fully embraced his role by training Shawn in basketball drills, traveling to Houston for school events and going on pizza runs with his grandson.
Reflecting on what it means to show up, Florian once shared that after his own father left the family, it was his grandfather who taught him how to be a good man. Now, he’s committed to doing the same for Shawn.
“You don’t have to be a father to help a boy become a good man,” he wrote on Instagram in 2023. “All it takes is a man that cares and want to be part of his life. At the end of the day it’s all about who steps up.”
The family grew once more when Isaiah and his wife, Kourtney Kellar, welcomed their son, Elijah James, on May 23, 2024.
Florian inspired his son's gameplay
Isaiah Hartenstein #55 of the Oklahoma City Thunder during Game One of the 2025 NBA Finals on June 5, 2025 in Oklahoma City, Oklahoma.
Isaiah Hartenstein #55 of the Oklahoma City Thunder during Game One of the 2025 NBA Finals on June 5, 2025 in Oklahoma City, Oklahoma.
Not only did Florian coach Isaiah, but the two also played together one year professionally in Germany — and he picked up a thing or two from him along the way.
“I think I got it from my dad,” Isaiah told the Oklahoma City Thunder's podcast in July 2024. “My dad, when he was playing, he was more just a super physical guy. So, I think he had a year where he like dislocated five guys’ shoulder just off a screen.”
“He always was very rough with me in practice,” he added. “We played together for one year so that wasn’t fun at practice either.”