"I lost my best friend today," Gaba's mother posted Tuesday on social media. "Your legacy will live on love bug."
Gaba was diagnosed with a malignant tumor in his eye when he was a baby and lost his sight. He later had operations, chemotherapy, radiation treatments and a bone-marrow transplant to treat tumors on his lungs, legs and neck.
Recent scans showed cancer had spread through his brain and lungs.
Gaba first became a fan and player favorite as a frequent caller on sports talk radio in Baltimore. His celebrity began when he secretly called into 105.7 The Fan while his mother was at work.
He parlayed that fame into appearances at professional sporting events and friendships with star athletes, including Ravens quarterback Lamar Jackson and Orioles star Trey Mancini.
In 2019, Gaba became the first person to announce an NFL Draft selection off a card written in braille. He previously threw out the first pitch at an Orioles game, caught a pass from Jackson at a Ravens practice and served as an honorary Ravens captain for a pregame coin toss.
"My heart is with Mo's parents and friends and family," Jackson told reporters Wednesday. "He was a great kid. He's a great soul."
Gaba had a special bond with Mancini, who is undergoing chemotherapy treatment after having a cancerous tumor removed from his colon in March.
"Your kindness, bravery and positivity has left a lasting impact on all of us who were lucky enough to have met you," Mancini tweeted Tuesday.
"You have truly made this world a better place."
Several athletes attended Gaba's graduation in June from Lindale Middle School He was inducted into the Orioles Hall of Fame hours before his death.
"Mo's positive energy has been constant throughout every battle and continues to bring the entire city of Baltimore together in the face of ongoing crisis," the Orioles said in a statement. "His unwavering positivity and kindness are qualities every Baltimorean aspires to emulate.
"Mo Gaba has impacted more people in his 14 years than most people do in an entire lifetime, and the Orioles are honored to forever celebrate him as a member of the Orioles Hall of Fame."