A friend

[Xinfu]

-He is ___.

If this person is one who places a heavy emphasis on friendship and will come to your aid when you are in trouble, what adjective should I use to depict him?

[Rusty]

a real friend
a dear ...
a trusted ...

a very good ...
a good ...

[Mariana]

A friend in need is a friend indeed.
maybe out of subject.. but I remember this quote which I like.

[Xinfu]

Thank you, Rusty, but I need an adjective rather than A + adj + FRIEND.

[Rusty]

I can't think of an adjective that is that specific. I'm afraid you'll need to use both an adjective and a noun in the subject complement.

true friend
real friend
loyal friend
reliable, dependable

You can use these adjectives alone, but they don't necessarily express the idea that he is also a friend.
He is true. (could mean 'a true friend', but could also mean 'true to his name/wife/faith')
He is real. (could mean other things than being a dear friend)
He is loyal. (could mean that he is loyal to his company - a dog is loyal)
He is reliable.
He is dependable.

We sometimes hear "He is Johnny-on-the-spot." This can describe a true friend, ready to come to your aid or provide service, but it can also describe anyone who is eager to help others (could be a complete stranger to you before the aid is given at just the right time).