Tom O'Brien was a jockey. The horse racing world mourn his death at 39 after a cancer diagnosis. The Racing Post called him a fantastic person. O'Brien secured victories at the renowned racing event. Several news outlets reported his death after a courageous battle with cancer. At Bangor, a colleague called him a champion and a brilliant rider. Yahoo News Australia said O'Brien was the another rider to die in a short span. Tributes continue in the world of horse racing.