The Olympic committee in the country they represent.
Each country's Olympic committee
international Olympic committee
their "sponsors"... aka wealthy people who brag about their "sponsorees"
The Olympics are not paid. The Olympic committee pays travel expenses.
The Government of the United States. US ambassadors have their own budget for their travel expenses.
The United States government does not pay their Olympic athletes. However, it is possible that an athlete will have a contract with a business, such as a shoe manufacturer or a swimsuit manufacturer, and that contract may have wording in it that says the athlete will be paid an amount for winning an Olympic event. The USOC - United States Olympic Committee - which is a private entity separate from the US Gov't - pays athletes for medals - $25,000 for gold, $15,000 for silver and $10,000 for bronze. Some athletes are invited to train at the US Olympic training facility run by the USOC and all expenses are paid, but the athlete must adhere to a strict training schedule and rules of the facility.
National football league ( A.K.A NFL)
1. Money left after a business pays expenses
This depends on what, if any, bonus the athlete's national Olympic committee pays out. For the USA, the USOC pays athletes $25,000 per gold medal, $15,000 per silver and $10,000 per bronze.