Exactly 50 years ago, Lewis Wolpert theorized that "morphogen gradient" might be a universal mechanism to explain the development of form and pattern. He metaphorized this idea using a visually simple and appealing representation: "The French Flag problem". In this lecture, we would look at the historical trajectory of how this theory found its footing in reality and how it is still being questioned and revised. I would use the patterning of spinal cord as a real life example to illustrate this historical trajectory. The paper, Briscoe et al., 2000, teased out the sophisticated process by which a sonic hedgehog gradient patterns the five progenitor zones in the ventral spinal cord. This work sits at the pinnacle of the first half of the "morphogen gradient" research and lays the foundation for the second half.