What vein runs from the upper thigh to the ankle?

The great saphenous vein runs from the upper thigh down to the ankle. It is the longest vein in the body, originating from the medial side of the foot, ascending along the inner aspect of the leg and thigh, and draining into the femoral vein near the groin. This vein plays a crucial role in returning deoxygenated blood from the lower extremities back to the heart.