Who are counterparties in swaps?

Can you please elaborate on the concept of counterparties in swaps? In a financial transaction such as a swap, who exactly are the counterparties involved, and what are their respective roles and responsibilities? Are there any specific requirements or qualifications that need to be met in order to become a counterparty in a swap agreement? Additionally, how does the identification and selection of counterparties impact the overall risk and success of a swap transaction?