A Physicists are interested in finding out what makes the universe tick. There are different kinds of physicists that study very different things. For instance, astro- physicists study the stars and planets. They are interested in how the stars and planets are born and what causes them to behave the way they do.
Many astronomers are physicists.
Then there are nuclear physicists. All physicists are interested in discovering the unknown whether it be a new star or planet or the nature of the particles that form the nucleus of the atom.