This paper presents a first-principles study on the interaction and charge transfer between graphene and various metal substrates using density functional theory (DFT). The research investigates how graphene interacts with different metals such as Al, Ag, Cu, Au, Pt, Co, Ni, Pd, and Ti, and how this interaction affects the electronic properties of graphene, particularly its Fermi level and doping characteristics. The study reveals that the bonding between graphene and certain metals (Al, Ag, Cu, Au, Pt) is weak, preserving graphene's unique electronic structure, including its conical points. However, charge transfer occurs, shifting the Fermi level by up to 0.5 eV. The crossover from p-type to n-type doping occurs when the metal's work function is around 5.4 eV, higher than that of free-standing graphene (4.5 eV). A simple analytical model is developed to describe this Fermi level shift based on the metal's work function. In contrast, graphene interacts more strongly with metals like Co, Ni, Pd, and Ti, leading to chemisorption and hybridization between graphene's p_z states and the metal's d states, which opens a band gap in graphene and significantly reduces its work function. This results in n-type doping of graphene in current-in-plane device geometries. The study also highlights the importance of considering the work function of the metal and the graphene-covered metal surface to understand the charge transfer and doping effects. The research provides insights into the electronic behavior of graphene in contact with different metals, which is crucial for the development of graphene-based electronic and spintronic devices. The findings are supported by detailed computational methods and comparisons with experimental data, emphasizing the role of metal-graphene interactions in determining the electronic properties of graphene.This paper presents a first-principles study on the interaction and charge transfer between graphene and various metal substrates using density functional theory (DFT). The research investigates how graphene interacts with different metals such as Al, Ag, Cu, Au, Pt, Co, Ni, Pd, and Ti, and how this interaction affects the electronic properties of graphene, particularly its Fermi level and doping characteristics. The study reveals that the bonding between graphene and certain metals (Al, Ag, Cu, Au, Pt) is weak, preserving graphene's unique electronic structure, including its conical points. However, charge transfer occurs, shifting the Fermi level by up to 0.5 eV. The crossover from p-type to n-type doping occurs when the metal's work function is around 5.4 eV, higher than that of free-standing graphene (4.5 eV). A simple analytical model is developed to describe this Fermi level shift based on the metal's work function. In contrast, graphene interacts more strongly with metals like Co, Ni, Pd, and Ti, leading to chemisorption and hybridization between graphene's p_z states and the metal's d states, which opens a band gap in graphene and significantly reduces its work function. This results in n-type doping of graphene in current-in-plane device geometries. The study also highlights the importance of considering the work function of the metal and the graphene-covered metal surface to understand the charge transfer and doping effects. The research provides insights into the electronic behavior of graphene in contact with different metals, which is crucial for the development of graphene-based electronic and spintronic devices. The findings are supported by detailed computational methods and comparisons with experimental data, emphasizing the role of metal-graphene interactions in determining the electronic properties of graphene.