From the Wikipedia article: https://en.wikipedia.org/wiki/Nobel_Memorial_Prize_in_Econom...
"It is not one of the prizes that Alfred Nobel established in his will in 1895, but instead was established 73 years later by a donation to the foundation from Sweden's central bank, the Sveriges Riksbank, on the bank's 300th anniversary."
From the criticism section:
In his speech at the 1974 Nobel Prize banquet Friedrich Hayek stated that had he been consulted on the establishment of a Nobel Prize in economics, he would "have decidedly advised against it" primarily because, "The Nobel Prize confers on an individual an authority which in economics no man ought to possess.... This does not matter in the natural sciences. Here the influence exercised by an individual is chiefly an influence on his fellow experts; and they will soon cut him down to size if he exceeds his competence. But the influence of the economist that mainly matters is an influence over laymen: politicians, journalists, civil servants and the public generally."
Less important, but relevant note about the name:
"Some critics argue that the prestige of the Prize in Economics derives in part from its association with the Nobel Prizes, an association that has often been a source of controversy. Among them is the Swedish human rights lawyer Peter Nobel, a great-grandson of Ludvig Nobel. Nobel criticizes the awarding institution of misusing his family's name, and states that no member of the Nobel family has ever had the intention of establishing a prize in economics."