Tom O'Brien was a jockey. British and Irish racing communities mourn his death at 39 after a diagnosis of cancer. The Racing Post called him a fantastic person. O'Brien won races at the renowned racing event. Several news outlets reported his death after a courageous fight with cancer. At Bangor, a close friend called him a hero and a brilliant rider. Yahoo News Australia said O'Brien was the second jockey to die in a short span. Tributes continue across horse racing.