Which agency is known for providing credit ratings?

The agency known for providing credit ratings is Moody's. This organization is one of the leading credit rating agencies globally, alongside others like Standard & Poor's and Fitch Ratings. Moody's assesses the creditworthiness of borrowers, which includes governments, corporations, and various financial instruments. Their ratings include letter grades that indicate the likelihood of default, helping investors make informed decisions regarding the risk associated with certain investments.

Fidelity Investments, while a reputable investment firm, primarily focuses on mutual funds and brokerage services rather than providing credit ratings. Goldman Sachs and Citi Group are both financial institutions primarily engaged in banking, investment, and asset management services but do not specialize in credit ratings like Moody's. Therefore, Moody's being directly focused on rating credit risk distinguishes it as the correct answer.