This is a debate that has been very present among psychologists. It is difficult to determine exactly what makes a person be kind or altruistic towards others. Sometimes, it might appear as if all the kind actions that people engage in are self-motivated.
However, I stand on the altruistic side. This is because there are plenty of examples in the world of people doing kind actions even when these do not benefit them. Moreover, there are people who are altruistic in cases where they might result worse off. For example, there are instances of people sacrificing their life in order to protect others. We can also use the examples of people who engage in political movements that benefit others, but might put themselves at risk. Therefore, it seems clear that it is possible for a person to be completely selfless.