What is the title given to second in command of the executive branch?

The person who is in command of the executive branch is the President. So, that means that the second in command of the executive branch would be the Vice President, the President's closest adviser and the President of the Senate. The Vice President actually is a very important job, because the Vice President, while he also serves in the executive branch, being President of the Senate, the VP is also extremely influential in Congress, which means the VP is vital in assisting the President with passing legislation.