He is very famous as he wrote a set of rules for living a more organised and therefore peaceful life. He also happened to be a Roman emperor so this was quite crucial for him to get everything done on time. He has much in common with Seneca and Stoicism in this respect. So the 2 are often read together to see how they compare and contrast.
A major point that Marcus mentions is to live your life as though you are going to die soon. While this may sound rather morbid and counterproductive; it is in fact sound advice. You are now motivated to do the most important things in life and that is to spend time with your family, friends and enjoying yourself by indulging in hobbies. You are no longer exclusively focused on hard work.
Marcus is part of the group of stoic philosophers that include Seneca the younger, Cato and Epictetus. There all from around the same time but with widely different viewpoints due to their unique lives. This helps enormously as you will always be able to find something useful since they will most likely have experienced it.