Which programming language was known for pioneering object-oriented programming?

Smalltalk is recognized for pioneering object-oriented programming (OOP). Developed in the 1970s by Alan Kay, Dan Ingalls, and others at Xerox PARC, Smalltalk introduced several key concepts that form the foundation of OOP, such as encapsulation, inheritance, and polymorphism. It allowed developers to model real-world entities as objects, enabling more organized and manageable code.

In contrast, Java and Python, while both modern and popular object-oriented programming languages, drew heavily from the foundational principles established by Smalltalk. HTML, on the other hand, is a markup language for structuring content on the web and does not possess any object-oriented programming characteristics. As a result, Smalltalk stands out as the language that first implemented the core ideas and methodologies of object-oriented programming, making it the correct answer in this context.