What do you mean by "rainmaker" or a piece of cake?

Today’s English:
24.1.2017
Have you heard the phrases -rainmaker and a piece of cake.  Probably yes. But they mean a little more than what you mean. Check it out.

Rainmaker – a person who generates income for a business/company by attracting clients/funds

Examples:
1. He is one of the senior rainmakers in our company.
2. You have to treat a person with due respect whether he is a person in the file room or a rainmaker.

A piece of cake – very easy

Instances:
1. The exam was really a piece of cake.
2. What about your new project? Is it a piece of cake or Herculean task?