What is the adjectival form of "initiative"?

Merriam-Webster says in its entry for
initiate that this
word can also be an adjective:

1. a : initiated or properly admitted (as to membership or an office)
   b : instructed in some secret knowledge
2. obsolete : relating to an initiate

However, this sense means introductory or preliminary, as in just getting
started. But that is not the sense that I am looking for here. I don’t want
an adjective derived from the verb initiate but rather one derived from the noun initiative.

I
would like to know the correctly derived adjective to fit this blank:

• This guy shows great initiative.
• This guy is ______.

I am not interested in meanings derived from the verb to initiate,
and to be frank I was quite surprised to find out those other senses.

My
question instead seeks an adjective whose meaning relates to what I believe
to be today’s dominant sense of the noun
initiative: the
one used to represent a positive quality in people who come up with their
own solutions, need not be told exactly what to do, etc. This is the sense
that Merriam-Webster gives as “energy or aptitude displayed in initiation
of action”.

In other words, I need something for this blank below:

• People who come up with their own solutions and need not be told exactly show great initiative.
• Such people are ________ people.