What is the title of the person in charge of a company?

What is the title of the person in charge of a company?
A company is a business structure which has legal status as an entity in its own right. A group of people called directors are responsible for running the company. One or more of these might be a managing director.
To a lesser extent, the shareholders are also in charge of a company - it is their invested funds which allow the company to function and they have an interest in how the company is run because the company needs to succeed for them to see a return on their investment.