The 21-year-old likes to hunt and fish, he works for the Harris County Sheriff's Office as a detention officer and he's a local boy who graduated from Lamar High School.
But O'Brien is also a special guy with a heartwrenching story, and friends are coming together this weekend to help him.
After high school, O'Brien went to a small, private university in Iowa for a year on a U.S. Army scholarship. But when he came home to Houston on his first summer break, he got some life-shattering news.
O'Brien was diagnosed with stage 4 Hodgkin's lymphoma.
From there, everything moved so quickly.
Chemotherapy failed. He had to quit school. Then, he was discharged from the Army ROTC program.
Doctors tried a stem cell transplant and then radiation, burning his skin and damaging his heart, lung, throat and stomach.
There was still no improvement.
The young man was put on trial drugs from across the country, but none of them helped. They tried 10 different chemo methods, which all failed to put him into remission.
O'Brien's doctors finally told his parents he was terminal and that more chemo would either kill him or make the cancer worse.
Earlier this year, doctors gave him until around mid-summer to live.
You might wonder if O'Brien has even an ounce of strength left after his ordeal, but his friends and family call him "inspiring."
"Thomas has inspired so many of us and has touched our lives in a way we will never forget," family friend Marie Henson told us.
O'Brien stays as active as he can. His Facebook profile shows photos of a skydiving adventure, his dog, his Jeep, his motorcycle and him spending time with family and friends.
While he may be battling cancer, he hasn't backed down from anything. He even successfully went through the application process at HCSO while he was fighting for his life.
"When it came time to fight cancer, he took it head-on with a positive attitude and shown even at his worst times, people can be their best," Henson said. "Thomas is a fighter, a hero, an inspiration to us all."
In his time of need, O'Brien's coworkers and loved ones are pulling together to support him.
A benefit has been organized for O'Brien on Sunday beginning at noon at Joe Kollz Rock'n Country Saloon on F.M. 1942 in Crosby. They'll have live entertainment, an auction, a 50/50 raffle, barbecue plates, dessert sales and even a pudding wrestling contest.
They're still collecting donations for the event until Friday. If you can donate auction items, baked goods or meat or condiments for the barbecue plates, call 281-806-6538. All donations are tax-deductible.