Al Asmaaul Husna - The most beautiful names
The Merciful, The One who has plenty of mercy for the believers.
Ar-Rahman argues for the attribute of the Self of Allah and Ar-Raheem for His active attribute.
Ref: (2:163)(3:31)(4:100)(5:3)(5:98) (11:41)(12:53)(12:64)(26:9)(30:5)(36:58)