He was promoted from minister plenipotentiary to full ambassador. ( submitted by pvzrsl)

Okay. Plenipotentiary's definition from answers.com is: adj. Invested with or conferring full powers: a plenipotentiarydeputy. n. , pl. -ies. So a Plenipotentiary would be someone that has many powers; ruler

The word plenipotentiary has two meanings,

As a noun, it refers to a person who has 'full powers'. In particular, the term commonly refers to a diplomat who is fully authorized to represent their government as a prerogative (i.e, an ambassador).

As an adjective, plenipotentiary refers to that which confers 'full powers'.

a representative with full power to negotiate and sign agreements

yes