Leadership is responsibility.
Responsibility, however, has two definitions:
1) Responsibility is having an obligation to do something about a particular situation.
2) Responsibility is being the primary cause of a particular situation.
The first definition of responsibility is what we mean when we ask, "who is in charge?" whereas the second definition of responsibility is what we mean when we ask, "who broke the lamp?" or "who built the fence?" One definition has to do with the present and the future, and who has the authority, the mandate, the charge, to make something happen in a particular way. The other definition has to do with the past and the present, who is to blame or credit for the way a particular thing happened or is happening. In some ways the first definition of responsibility is actually about accepting blame/credit before the fact!
Leadership is about both kinds of responsibility.
A leader takes the blame for whatever happened on their watch. Although a good leader will pass along the credit to those around them, a good leader doesn't shirk blame. But assigning and taking blame and/or credit is actually not the primary way in which leaders take responsibility.
Leadership is ultimately about the first kind of responsibility.
To be a leader is to see oneself as the primary person tasked with accomplishing something. This doesn't mean a leader does everything themselves, (creating teams and delegating tasks are encouraged) but the leader is the one who says, "Yes, I am responsible to see it done. If it doesn't get done, and done right, I will be to blame."