One of the most poignant sentences in the story of The Happy Prince by Oscar Wilde, and one which can sum up the essence of both story and character is when, at the end, the Art Professor at the University says:
As he is no longer beautiful he is no longer useful
The prince was once a very happy one, and had been modeled in gilt gold leaves for all the world to see. Everything about him was materialistically perfect: Bejeweled eyes and fingers, gold all over, and so on.
Yet, the prince was only superficially happy and perfect. From his height and position he could see how the poor lived and how miserable their conditions were. Hence, he asked a swallow that rested on him to start giving out his gold and jewels to the poor so that they can have a better life.
This right here tells us the nature of the prince: He is an individual idealized by society, put on a pedestal by his peers, and wrapped in luxury by his own destiny. Yet, far from wanting all this, there is a side of him that advocates in favor of the least lucky, and wishes for equality for all.
He is obviously sensible to the needs and wants of others, and he opts to self-sacrifice in order to save those who have less than he did. For this, we could say that he is altruistic, kind, and sacrificial. Hence, the prince is more of a martyr than any other thing. Once his gold was all gone, he was considered nothing.