Mark Todd's Beijing Olympic horse Gandalf has died.

The 11-year-old grey has had to be put down because of a serious neurological disorder.

Gandalf has recently suffered seizures which saw him become blind in his right eye and a danger to himself and his handlers.

Mark Todd was naturally very upset by the loss: "It was a very hard decision to make but the wellbeing of the horse is what we have to consider foremost. It's also sad for New Zealand eventing to lose a horse of his calibre. Unfortunately we didn't get to see the best of him."

In one of the most exciting and bold sporting decisions of the 21st Century, it was in November 2007 where the seeds of a comeback for the Rider of the 20th Century were planted, over a few glasses of wine with fellow eventing enthusiasts.

Gandalf is credited with Mark's phenomenal come-back after an eight year absence: Speaking at the time, he said: "He was available to be bought, so I flew up to Auckland, tried him out, had him vetted and it all happened very quickly. There wasn't a lot of planning involved, it all just happened. I'm looking at this as a challenge, as a bit of fun and I'm putting absolutely no pressure on myself. If it happens, it happens and that's how I'm approaching it."

"Gandalf has got a good record," Mark said. "He's a very good jumper and he looks after himself so that sounds good to me. I might need a little looking after."

Some 24 years after he won his first gold medal at Los Angeles and after an eight year retirement, Mark made a return to the sport. During his time away from eventing Todd trained racehorses, including NZ Oaks winner Bramble Rose and Wellington Cup winner Willy Smith.

Born in 1998, Gandalf was by the pinto sporthorse sire Pintado Desperado and out of the thoroughbred mare Princess of Power (Galaxy Bound). He was bought as a yearling by Anglea Lloyd, who produced him to three star level.

Mark formed a successful partnership with Gandalf, which ultimately saw them qualify for last year's Olympics where they finished 17th out of 70 competitors.