This paper investigates a novel reheating mechanism in cosmology, where the universe transitions from an inflationary state to a radiation-dominated state through the resonant annihilation of the inflaton field via a massive scalar mediator. The inflaton field, oscillating in a monomial potential, experiences a time-dependent mass that leads to resonance phenomena during reheating. This resonance enhances the production of the mediator, which then decays into Standard Model (SM) particles, contributing to the thermal bath. The resonance significantly affects the evolution of the SM temperature, creating a non-trivial temperature profile that differs from the standard power-law behavior. The study explores the implications of this resonant reheating scenario for dark matter (DM) production. The mediator can play a key role in generating DM, particularly through the freeze-in mechanism, where DM is produced via interactions with the SM thermal bath or inflatons. The resonance during reheating modifies the freeze-in dynamics, leading to new and interesting behaviors in DM production. The paper also discusses the potential observational signatures of this scenario, including the generation of primordial gravitational waves (GWs) with a blue tilt, which could be detectable by next-generation GW detectors. The paper presents analytical and numerical solutions for the evolution of the inflaton and SM radiation energy densities, as well as the SM temperature, during reheating. These solutions reveal how the resonance affects the temperature evolution, with a maximum temperature occurring near the end of reheating. The study also examines the impact of resonant reheating on DM production, showing that the DM abundance depends on the reheating dynamics and the parameters of the mediator and inflaton. The results indicate that resonant reheating can lead to a higher reheating temperature compared to non-resonant scenarios, and that the DM production can be significantly modified by the presence of the resonance. The paper concludes that resonant reheating is a viable and testable scenario, with potential observational signatures that could be probed by future gravitational wave detectors.This paper investigates a novel reheating mechanism in cosmology, where the universe transitions from an inflationary state to a radiation-dominated state through the resonant annihilation of the inflaton field via a massive scalar mediator. The inflaton field, oscillating in a monomial potential, experiences a time-dependent mass that leads to resonance phenomena during reheating. This resonance enhances the production of the mediator, which then decays into Standard Model (SM) particles, contributing to the thermal bath. The resonance significantly affects the evolution of the SM temperature, creating a non-trivial temperature profile that differs from the standard power-law behavior. The study explores the implications of this resonant reheating scenario for dark matter (DM) production. The mediator can play a key role in generating DM, particularly through the freeze-in mechanism, where DM is produced via interactions with the SM thermal bath or inflatons. The resonance during reheating modifies the freeze-in dynamics, leading to new and interesting behaviors in DM production. The paper also discusses the potential observational signatures of this scenario, including the generation of primordial gravitational waves (GWs) with a blue tilt, which could be detectable by next-generation GW detectors. The paper presents analytical and numerical solutions for the evolution of the inflaton and SM radiation energy densities, as well as the SM temperature, during reheating. These solutions reveal how the resonance affects the temperature evolution, with a maximum temperature occurring near the end of reheating. The study also examines the impact of resonant reheating on DM production, showing that the DM abundance depends on the reheating dynamics and the parameters of the mediator and inflaton. The results indicate that resonant reheating can lead to a higher reheating temperature compared to non-resonant scenarios, and that the DM production can be significantly modified by the presence of the resonance. The paper concludes that resonant reheating is a viable and testable scenario, with potential observational signatures that could be probed by future gravitational wave detectors.