There are many horses that have been recorded as exceptionally tall.
Here are a few things to consider:
* Height is recorded in hands, not inches: A hand is 4 inches, so a horse that stands 21 hands tall is actually 84 inches tall.
* The world record for the tallest horse ever recorded belongs to a Shire horse named Sampson. Sampson was recorded at 7 feet 2 inches (21.8 hands) tall.
* "Dr Le Gear" might be a misremembered name. There is no widely known horse with that name that holds the record for height.
If you have any more information about the horse you are referring to, I may be able to help you find it.