Final answer:
The key role of an investment banker is to underwrite securities, facilitate mergers and acquisitions, and manage investment portfolios. They do not provide legal advice.
Step-by-step explanation:
The key role of an investment banker is to underwrite securities, meaning they help companies issue and sell securities to investors. They also play a vital role in mergers and acquisitions, facilitating the buying and selling of companies. Another important responsibility of an investment banker is managing investment portfolios for clients.
However, providing legal advice is not a key role of an investment banker. While investment bankers may have a basic understanding of legal issues related to finance, they typically work with legal professionals to ensure compliance with regulations, but they do not provide legal advice themselves.