Merriam-Webster says "initiative" can be also an adjective, however, it is adjectival from "to initiate", meaning "introductory" or "preliminary". What is then the correct adjective of "initiative" as in "this guys shows great initiative"? This guy is...?
Edit: I am afraid I did not phrase my question clearly: I am not interested in the meanings derived from "to initiate", actually I was quite surprised to find out this other meaning of the word. My question relates to -- what I believe is today's prime meaning of the word -- initiative as a positive quality in people who come up with their own solutions, need not to be told exactly what to do, etc. These people are ...?