who was the duke of cardigan and why was he so named?

Answer 1

He wasn't a Duke, but there have been several Earls of Cardigan (Cardigan being a town in Wales); in the late 1800s, the title became subordinate to that of the Marquess of Ailesbury and is now given to the heir to that title.

The best-known Earl was the 7th, James Brudenell, the incompetent military leader who led the Charge of the Light Brigade.

Answer 2

I never heard of a duke of Cardigan, there is (was) an Earl of Cardigan.

Cardigan is a town in Wales. If you're thinking of the sweater named after him, he invented it for the British Army uniform during the late 1800's, because the sleeves (courtesy of Lord Raglan's design - raglan sleeves) have less bulk and it fits better under a topcoat.

Answer 3

There was only an Earl of Cardigan. Unlike nowadays, when new peers are unimaginative and just call themselves 'Lord Smith' or 'Lord Jones', in the 19th century new lords would call themselves after a place where they were from, where they owned land, where they won a battle or perhaps where they intended to settle one day.The first Lord Cardigan would have had some such connection with the aforementioned town in Wales.