Atomically dispersed metallic materials offer unique advantages in various applications. Multimetallic single atom/cluster (SA/AC) materials have shown potential beyond monometallic counterparts, with applications in catalysis, electronics, and environmental protection. Despite challenges in their synthesis, a novel energy-selective-clustering method has been developed to fabricate a diverse library of bi-/multi-metallic SA/AC materials on a carbon support. This approach allows for the integration of multiple metal elements with varied properties on a single substrate, offering new possibilities for structure-property relationships. The study focused on hydrogen electrocatalysis, highlighting the potential of multimetallic materials for producing green hydrogen efficiently. Results included the fabrication of 23 bimetallic and 17 trimetallic/quinary/septenary-metallic SA/AC composites with promising electrocatalytic properties. High-performance catalysts for oxygen reduction and evolution reactions were also developed through composition modification. The methodology's mechanism is based on the cohesive energy controlled selective-clustering of metals, enabling the formation of single atoms or clusters based on metal cohesion and metal-support interaction. This innovative approach opens new avenues for fabricating multimetallic atomically dispersed materials with diverse applications in sustainable energy and beyond.