In Stanley Kubrick’s 2001: A Space Odyssey, the mysterious black object found by the apes is the Monolith.
The film opens in prehistoric Africa, where a group of apes encounters a tall, rectangular black structure. Soon afterward, one ape uses a bone as a tool and weapon, suggesting that the object has stimulated a major evolutionary leap. The sequence links the Monolith with humanity’s technological development.
The Monolith reappears at important points in the story, including near the Moon and close to Jupiter. Its purpose is deliberately mysterious, and the film does not provide a conventional spoken explanation. Arthur C. Clarke’s accompanying novel gives more explicit context, but Kubrick’s film relies heavily on visual symbolism and ambiguity.
A common mix-up is calling it an obelisk. Although its shape resembles one, the film and its related discussions generally identify it as the Monolith. Its smooth black surface and precise geometry are central to its visual identity.