What is a friend?

"What is a friend? A single soul dwelling in two bodies." ~ Aristotle

"A friend loveth at all times, and a brother is born for adversity." ~ Prov 17:17

"A man that hath friends must shew himself friendly: and there is a friend that sticketh closer than a brother." ~ Prov 18:24

"Remember, no man is a failure who has friends." ~ It's a Wonderful Life