what was the most significant relationship chris formed along his journey

This is really up to your opinion. I might consider Ronald Franz. He is an eighty-year old devout Christian and soldier who picks McCandless up hitchhiking and takes a strong liking to him. He has lost his wife and children long ago, and so feels a fatherly affection for Chris, whom he offers to adopt. After hearing of Chris’s death, he stops believing in God.