Gregory Williams outlines successful leadership in turning around several failing projects, notably the Nationwide Building Society's SAP transformation, where he established a PMO and implemented a structured plan that eliminated critical failures. His initiatives with Aviva in outsourcing resulted in significant cost savings and optimizations, while his work with HBOS led to the creation of a new business banking model within a tight timeframe. Williams emphasizes expertise in cultural change management, process optimization, and critical path management for SAP implementations.