Also a very specific type of servant in Regency era England; a tiger was a well-turned out groom suitable for public display.
Grooms were ubiquitous in days when all travel was done by horses and carriages, but a tiger was specifically a groom that rode on a small standing platform on the back of a small carriage such as a cabriolet or a curricle. Because of the small size of the carriage, a tiger was nearly always a boy or man of slight build, ideally under five foot tall. The tiger was highly visible, and as these carriages were used when the wealthy wanted to travel about town (which usually meant London), it was important that they were presentable.
"The tiger was a Lilliputian phenomenon, with apparently three tightly fitted natural skins: one of leather, bifurcated for his neithers: another of pepper and saltcloth for his coat: a third of jetty-black surmounted with brown streaks for top boots. Portions of his epidermis they must have been; for although, if artificial, he might have got them on, it was beyond the range of human possibility that he could ever get them off. Stay, an additional article must be mentioned in regard to his buckskin gloves. With shining livery buttons, with tight little belt around his tight little waist, and with a hat bound with silver cord, this domestic was surely the tightest tiger that ever was seen.
--All the year round: a weekly journal, Volume 11 By Charles Dickens, 1864
A wealthy peer might indulge himself (or indeed herself; a tiger was an acceptable chaperon for a lady of quality) in a matched pair of tigers. This was clearly a sign of great wealth, as a carriage pulled by two horses does not require two grooms. Sadly, it was not feasible to adorn your cabriolet with more than two tigers, both for reasons of weight and standing room. Tigers were not actually that important, as one can manage a jaunt out during the fashionable hour without someone to manage the horses; a tiger also has the disadvantage of occupying the same space as the folded top, so that the carriage must ridden 'half-struck'. This was socially acceptable, but not always desirable.
'Tiger' was first used in this sense in 1817, and continued to be used until carriages fell out of common usage. At times other outdoor servants in spiffy livery might be referred to as tigers, but this was uncommon.