John Rawls was one of the bets known proponents of rights theories in the twentieth century. His main thesis is found in A Theory of Justice. I remember that best for the man on the moon thought experiment. Rawls argued that an ideal (just) society would be formed when a person was asked to form that society knowing that they would be in that society, but without knowing what individual characteeristics they would adopt. I would structure a society so that everyone was treated fairly, because I would not know who I would become (most people struggle with this, because they assume that personal characteristics, such as intellect and motivation would be taken with them; when done properly, this is not the case).
His resultant theory of justice is heavily based on the social contract and rights of people.
Here is a fairly good review of his life's work, and his critics.