Which version of Mac OS X introduced built-in support for iCloud?

The version of Mac OS X that introduced built-in support for iCloud is Mac OS X 10.7, named Lion. This operating system was released in July 2011 and marked a significant integration of Apple's cloud services, enabling users to store files, photos, and other data in iCloud seamlessly. This built-in support allowed for automatic synchronization across multiple devices, facilitating a more cohesive user experience.

Understanding the context of iCloud's introduction helps clarify the importance of the Lion release in Apple's ecosystem. While Mountain Lion further improved upon these features and introduced new functionalities, it was Lion that fundamentally integrated iCloud services during its initial rollout. In contrast, Panther and Snow Leopard predate the iCloud announcement and did not feature similar cloud integration capabilities.