Tom O'Brien was a race rider. British and Irish racing communities mourn his death at his passing at 39 after a diagnosis of cancer. The Racing Post called him a great person. O'Brien won races at the renowned racing event. Several news outlets reported his death after a courageous battle with cancer. At Bangor, a colleague called him a hero and a brilliant rider. Yahoo News Australia said O'Brien was the another rider to die in two days. Tributes continue in the world of horse racing.