This study reports the realization of an insulating massive Dirac fermion state on the surface of a magnetically doped topological insulator, Bi₂Se₃. The state is achieved by breaking time-reversal symmetry (TRS) through magnetic doping and positioning the Fermi energy (E_F) within the Dirac gap. The surface state of topological insulators is characterized by a massless Dirac fermion, but when TRS is broken, a gap opens at the Dirac point, making the fermion massive. This state is important for studying topological phenomena relevant to both condensed matter and particle physics. Topological insulators are a new state of matter with robust surface states that are immune to localization as long as TRS is preserved. Magnetic doping breaks TRS, leading to a gap at the Dirac point and a massive Dirac fermion state. The study shows that in Bi₂Se₃, the Dirac point is located within the bulk gap, making it a better candidate for realizing the insulating massive Dirac fermion state compared to Bi₂Te₃. The research uses angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structure of Bi₂Se₃. The results show that the surface state band (SSB) evolves from the Dirac point to a hexagonal shape at E_F. The SSB remains convex even in the presence of the bulk conduction band (BCB), which is different from Bi₂Te₃. This difference affects experimental observations, such as scanning tunneling microscopy/spectroscopy (STM/STS). The study confirms the surface nature of the hexagonal SSB by showing that its shape does not change with photon energy. The TRS protection of the Dirac point is lifted by magnetic doping, resulting in a gap that separates the upper and lower branches of the Dirac cone. The gap size is determined by fitting the twin-peak structure in the energy distribution curve (EDC) with two Lorentzian peaks. The study also shows that by introducing Mn dopants, the E_F can be tuned into the SSB gap, realizing the insulating massive Dirac fermion state. This state supports topological phenomena such as the image magnetic monopole effect and the half quantum Hall effect. The study further demonstrates that the E_F can be tuned to different regions by surface or bulk doping, enabling a full range of control over the electronic properties of the material. This tunability is crucial for applications in spintronics and quantum information processing.This study reports the realization of an insulating massive Dirac fermion state on the surface of a magnetically doped topological insulator, Bi₂Se₃. The state is achieved by breaking time-reversal symmetry (TRS) through magnetic doping and positioning the Fermi energy (E_F) within the Dirac gap. The surface state of topological insulators is characterized by a massless Dirac fermion, but when TRS is broken, a gap opens at the Dirac point, making the fermion massive. This state is important for studying topological phenomena relevant to both condensed matter and particle physics. Topological insulators are a new state of matter with robust surface states that are immune to localization as long as TRS is preserved. Magnetic doping breaks TRS, leading to a gap at the Dirac point and a massive Dirac fermion state. The study shows that in Bi₂Se₃, the Dirac point is located within the bulk gap, making it a better candidate for realizing the insulating massive Dirac fermion state compared to Bi₂Te₃. The research uses angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structure of Bi₂Se₃. The results show that the surface state band (SSB) evolves from the Dirac point to a hexagonal shape at E_F. The SSB remains convex even in the presence of the bulk conduction band (BCB), which is different from Bi₂Te₃. This difference affects experimental observations, such as scanning tunneling microscopy/spectroscopy (STM/STS). The study confirms the surface nature of the hexagonal SSB by showing that its shape does not change with photon energy. The TRS protection of the Dirac point is lifted by magnetic doping, resulting in a gap that separates the upper and lower branches of the Dirac cone. The gap size is determined by fitting the twin-peak structure in the energy distribution curve (EDC) with two Lorentzian peaks. The study also shows that by introducing Mn dopants, the E_F can be tuned into the SSB gap, realizing the insulating massive Dirac fermion state. This state supports topological phenomena such as the image magnetic monopole effect and the half quantum Hall effect. The study further demonstrates that the E_F can be tuned to different regions by surface or bulk doping, enabling a full range of control over the electronic properties of the material. This tunability is crucial for applications in spintronics and quantum information processing.