CHINO HILLS -- When Matthew Greathouse met Karla Rosen in 2005 she was wearing a wig.
"Then she took it off and that was the first time I saw anyone with cancer at such a young age," said Greathouse, 18, of Chino Hills.
"I remember getting introduced to what was going on. My family and I weren't very close to the Rosens, but our relationship grew since then.
"It was inspiring to me that Karla was battling so hard against it, and it's changed my life since then. Once I found out about cancer and how it really affected the family and Karla it left an imprint."
Karla passed away on Feb. 5, 2006 of brainstem glioma, or an inoperable brain cancer.
She was 15 and Greathouse was 11.
In the spirit of the holiday season, we searched for ordinary people making an impact -- with little or no fanfare -- on communities across the greater Los Angeles area:
Inspired by Karla's battle, her parents started The Let It Be foundation, a nonprofit that assists families who have a child with a life-threatening illness.
The foundation's mission reflects the life-changing impact that illness can have on the family dynamic.
Greathouse was too young to volunteer with the organization's junior advisory team when he was in the sixth grade. But a year later, he quickly joined the cause. He is now a junior advisory team captain.
Other Let It Be captains: Steven Bock, Thomas Zorrilla, and Kacie Finneran of Chino Hills High; Marissa Amorelli of St. Lucy's Priory High School in Glendora; and Erica March who attends Rosary High School in Fullerton.
There are more than 40 Let It Be volunteers.
"Back when it started, Ruthe Rosen (Karla's mother) was my neighbor, and the whole story was so close to me and my family, and when Let It Be was founded, I want to get involved right away," he said.
"When I could volunteer, I jumped at it, and ever since then, it's been a part of my life. Just being able to give back to the community, making kids and their families lives better, I enjoy doing."
To date, Greathouse has donated about 1,000 hours of his time to the foundation, making him one of their most active members.
In September, he was honored as the 2012 Los Angeles County Fair's Young Adult Community Hero for Chino Hills.
Some of the volunteer activities include community-wide lemonade stands, garage sales, talent shows, holiday basket deliveries, room makeovers and holiday home decorating.
Greathouse and other Let It Be volunteers recently wrapped gifts at the Shoppes in Chino Hills at a Let It Be fundraiser.
"Finding a balance as a young person is an art, and Matt does a great job of balancing himself as a young person," said Ruthe Rosen, co-founder of Let It Be.
"He puts in effort and pride in his commitment with our Let It Be foundation families, staff and team."
But Greathouse said it's through Ruthe Rosen's compassion, passion and commitment that he is able to reach out to families in need.
"She's the biggest inspiration in my life," he said.
Greathouse is also busy as a senior at Chino Hills High School. He serves as the Associated Student Body treasurer, taking three Advance Placement classes, keeping a 4.1 grade point average and applying for colleges.
Through an early decision application, Greathouse expects to find out if he's been accepted to Princeton University on Tuesday. He's planning to major in astrophysics.
In addition to Ruthe Rosen, Greathouse said his older sister Laura has been a big influence in his life.
"She always had that passion to get involved with everything and that drove me to give back," he said.
Chino Hills High's activity director Janet Roberts said Greathouse has been a true role model on the high school campus.
"He's approachable and he generally cares about the kids on campus and they know it," Roberts said.
"When he talks to someone he's listening to them. He makes other students feel important and not a lot of students can do that, and I think that's why students navigate to him."
Even if Greathouse moves away for college, he said he hopes to spread the mission of the Let It Be Foundation by creating a club.
"It would be amazing to get the foundation out to different states," he said. "Because I don't think I could ever stop giving back to people."
For more information about The Let It be Foundation, visit theletitbefoundation.com.
Reach Canan via email, call her at 909-987-6397 ext. 425, or find her on Twitter @ChinoValleyNow.