I think you can tell a lot about a person by what he values in a friend, and you probably never know a man until you've seen him with his best friend either. I found something about Karl Barth's description of his close friend Eduard Thurneysen fairly moving:
"All my personal impressions of him can be summed up in the word openness . . . Thurneysen has the rare gift of being able to learn from others and, moreover, to learn from a person just what is worth learning from him. He then brings it alive in his own way. However, he is hardly ready to settle for well-defined positions or trends. If you are looking for his views it is no use expecting them always to be once and for all in one particular place. For all his decisiveness, he is a volatile man, and is always apt to spring surprises over points of detail . . .
[H]e gets on with people in an astonishing way. He can put himself in their place, walk with them and help them by understanding them (though from a more lofty vantage point and in a transfiguring light). He shares their sorrow or their joy. The very evident criticism which he brings to bear on them is almost always a radical, immanent criticism which is constructive by being comforting, helpful and friendly . . .
His study and indeed his view of the church and the world is like Noah's ark: all kinds of animals can enter and leave again, saved for the time being, under the sign of the rainbow which binds heaven and earth together" (From E. Busch, p. 74).