One friend's absurdist sense of humor seems very familiar. Though I would be hard pressed to actually remember specific examples from our childhood, it's one of his identifying characteristics. Another friend shared some traumatic experiences he had after I moved away. Though I had absolutely no connection to him during those times, through his story I recognized his compassionate personality. Of course, at eleven years old, I didn't understand those traits, but as an adult, I remember the common sensibilities that brought us together.
Finally, there's one kid of which I remember very little beyond his name and one or two specific memories, perhaps dating back as far as first grade. But in corresponding with him, I remembered the basics - a nice kid with a particularly friendly personality.
Though I can see the common threads of my own personality through my lifetime, It still seems surprising to recognize this friends at such a fundamental level.