EQUESTRIAN rider of the 20th Century, Mark Todd, this week faced the sad decision to have his 11-year-old Olympic horse NZB Gandalf put down as the result of a serious neurological disorder.

Gandalf was Todd's 2008 Olympic mount, and had recently suffered seizures, which made him blind in his right eye.

He had become a danger to himself and his handlers, Todd said.

"It was a very hard decision to make but the wellbeing of the horse is what we have to consider foremost," he said.

"Unfortunately we didn't get to see the best of him."

After an eight-year retirement, Todd made a return to equestrian competition in November 2007 - some 23 years after he won his first gold medal at Los Angeles.

During his time away from eventing, Todd trained racehorses, including NZ Oaks winner Bramble Rose and Wellington Cup winner Willy Smith.

In nine months, Todd and Gandalf qualified for the 2008 Olympic Games and were selected to represent New Zealand. The pair finished 17th out of 70 competitors.

Despite Gandalf's untimely demise, Todd will continue his bid to represent New Zealand at London in 2012.