A real estate agent has a license, issued by the state, that allows them to act as a fiduciary agent for principals (people) in real estate transactions UNDER the supervision of a Broker.
A Broker is licensed to act as a fiduciary for principals in a real estate transaction without supervision and can supervise other licensed agents. All contracts are between Brokers and principals.
Only a licensed Broker can manage rental property.
A Realtor is a real estate agent that is a member of the National Association of Realtors. Not all licensees are Realtors but all Realtors are licensees. Realtors swear an oath to abide by a code of ethics that is above and beyond what the law demands of licensees.
From all of this you can deduce that a Brokerâ€™s license is harder to get, requires more experience, knowledge and expertise.
A brokerage is a firm lead by a licensed broker and has other licensees under supervision. The agents are all independent contractors.
If a licensed Broker is working with another broker they are referred to as a broker associate. I have a brokerâ€™s license and am associated with Coldwell Banker.