Whistlejacket was foaled in 1749. His most famous victory was in a race over four miles for 2000 guineas at York in August 1759. Stubbs's huge picture was painted in about 1762 for the 2nd Marquess of Rockingham, Whistlejacket's owner and a great patron of Stubbs.
According to some writers of the period the original intention was to commission an equestrian portrait of George III, but it is more likely that Stubbs always intended to show the horse alone rearing up against a neutral background.
Miranda Hinkley: ‘Stubbs’s Horse’ by Roger Robinson.
Looking at Stubbs’s horse in the dark it becomes clear
He was no muscular glamourist, no fetishizer of fur and skin,
Convinced that the body was the host to the horse’s spirit,
He began making martyrs of horses, subjecting them to juggler death,
Beads of sweat rolling down their barrelled torsos,
Their eyelashes fluttering with a flourish,
Pumping them with warm tallow till their pulsing veins and arteries slowly came to a halt,
Suspended in a standing or a trotting pose by a series of hooks and tackles amid buckets of clotting blood,
Working his way through muscle by muscle, bone by bone,
Dissecting and designing limbs,
First stripping off the skin and other layers of muscle,
Turning pages in the book of horse.
So that even in the dark of the museum I can feel this horse breathing.
From The National Gallery Podcast: Episode Seven, May 2007