What is important in a friend ?

Friendship is indispensable to human which is a social being. Social means, it can't live solitarily. People need other people in every period of their lives. Sometimes for help in tough moments, sometimes for sharing feelings, for feeling sad for something bad or feeling happy for something good together, they need somebody around.
Friends are important for shaping one's character. We gain lots of our characterical attributes through our friends. Many habits transmit to people from their friends. If somebody chooses bad people as friends, he also becomes bad; if he chooses good people as friends, he becomes good this time.
I think, for someone to be a real friend, he must be reliable, he must be sincere towards people around him. Because trust is crucial for people's relationships and nothing can be achieved, if there isn't trust between people. If I don't trust somebody, I can't be close to him, I can't be together with him or I can't tell my secrets to him.