Who invented the stamp..?

“A bit of paper just large enough to bear the stamp, and covered at the back with a glutinous wash” – this was Rowland Hill’s proposal that eventually became the world’s first adhesive postage stamp. Issued in 1840 and known as the Penny Black, it prepaid postage up to half an ounce in weight to anywhere in the United Kingdom.

Why is there no country name on UK stamps..?

Because Royal Mail invented the stamp, it alone does not have to print the country of origin on its stamps. All other countries must do so.