Robert Gagne is considered a leading contributor to instructional design theory. His model is based on how information is processed mentally and focuses on arranging instructional events to achieve learning outcomes. Gagne identified nine events of instruction, including gaining attention, informing learners of objectives, eliciting performance, and providing feedback. His theories provide a framework for effective lesson planning and systematic instruction across domains like military training, engineering, and healthcare. Applying Gagne's nine steps can help ensure lessons are structured to meet learning objectives and achieve understanding rather than just recall.