You’ll come in and you may be a junior or assistant account manager, then you become an account manager. After that you’d become an account director, and then a business unit director where you have direct reports and a portfolio of clients. From there, you may move on to EXCO or a managing director role.
At director level you become far more responsible for the budgeting and the billing. You also meet the most senior clients at their level, as you’re delivering not only your profit but also the client’s growth. At a senior level, it’s managing staff, budgets, new business and new projects. The reason that people end up being managing directors is that you’re growing people and profits and maintaining existing clients and new business.