Gang of Four (GoF)
Nickname for the authors of "Design Patterns: Elements of Reusable Object-Oriented Software" (1994) — Gamma, Helm, Johnson, Vlissides. And the book itself.
Defined 23 patterns in three categories: creational (Factory, Singleton, Builder, Prototype, Abstract Factory), structural (Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy), behavioural (Chain of Responsibility, Command, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor, Interpreter).
Influential but criticised: many patterns are language workarounds for C++/Java limits. In functional languages they're half-redundant. Still the vocabulary every senior engineer is expected to know.