Final answer:
An Investment advisor is responsible for making the buy and sell decisions in a portfolio, differing from foreign direct investments which are more complex and take longer to manage.
Step-by-step explanation:
The individual who runs the portfolio and makes the buy and sell decisions is called an Investment advisor. The role of an investment advisor is crucial as they have managerial responsibility and are directly involved in the decision-making process regarding which securities to purchase or sell. In the context of portfolio investments, actions can be executed rapidly, often with just a phone call or several keyboard clicks. In contrast, foreign direct investments, like purchasing a company in another country, are typically more complex and time-consuming.