Three different cathodic materials for the hydrogen evolution reaction (HER) consisting of Ru nanoparticles (NPs) supported onto a bare and two doped reduced graphene oxides (r-GO) have been studied. Ru NPs have been synthesized in situ by means of the organometallic approach in the presence of each reduced graphene support (bare (rGO), N-doped (NH2-rGO) and P-doped (P-rGO)). (HR)TEM, EDX, EA, ICP-OES, XPS, Raman and NMR techniques have been used to fully characterize the obtained rGO-supported Ru materials. These materials have been deposited onto a glassy carbon rotating disk electrode (GC-RDE) to assess their HER electrocatalytic activity at acidic pH. The results show that all three materials are stable under reductive conditions for at least 12 h, and that the heteroatom-doping of the graphene structure extremely increases the activity of the electrodes, especially for the case of Ru@P-rGO, where the overpotential at -10 mA·cm-2 decreases to only 2 mV. Realistic (based on experimental compositional data) modeling of the three rGO supports combined with DFT computational analysis of the electronic and electrocatalytic properties of the hybrid nanocatalysts allows attributing the observed electrocatalytic performances to a combination of interrelated factors such as the distance of the Ru atoms to the dopped rGO support and the hydride content at the Ru NP surface.