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However, realizing such robots remains challenging due to the lack of mechanically intelligent bodies with abundant tunable parameters\u2014such as tunable stiffness\u2014which is a critical factor akin to the programmable parameters of a neural network. We introduce an elastic rolling cam (ERC) with accurately inverse-designable rotational stiffness. The ERC can closely replicate 100,000 randomly generated stiffness profiles in simulation. Prototypes ranging from millimeters to centimeters were manufactured. To illustrate the mechanical intelligence encoded by programming the ERC\u2019s stiffness response, we designed a bipedal robot with optimized ERC passive knees, achieving energy-efficient, open-loop stable walking across uneven terrain. 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