Normally we're going to like people who are people oriented and have some empathy for other people. If they are reclusive, sociopathic, or totally selfish, we won't like them. We like people who are warm, caring, and giving. With the autistic man, we were intrigued by his plight and were sympathetic toward him and his brother. With the hero, we saw through his rough exterior to the goodness inside.
Some personality traits are more difficult to pin down.
If a character or person is genuine, we are more apt to like him. Not pretending to be something they are not. Not false, like people who will lead you on or are two-faced. Self-assurance is a trait likable characters often have, but this doesn't always hold true. Attitude is another trait that is difficult to pin down.