Tom O'Brien was a race rider. British and Irish racing communities mourn his death at 39 after a cancer battle. The Racing Post called him a great person. O'Brien won races at the Cheltenham Festival. The Guardian and 7NEWS reported his death after a courageous battle with cancer. At Bangor, a close friend called him a champion and a skilled jockey. Yahoo News Australia said O'Brien was the another rider to die in a short span. Tributes continue across horse racing.