The Underground Muon Detector (UMD) of the Pierre Auger Observatory is designed to conduct a precise assessment of the muon component within air showers from cosmic rays with energies surpassing $10^{16.6}\mathrm{\, eV}$. The muon content serves as a valuable indicator of the mass composition of primary particles. It consists of segmented modules of plastic scintillation bars buried at a depth of 2.3$\,$m to shield them from the electromagnetic component of the showers. This work is an overview of the characteristics of the detector regarding its mechanics and electronics, the main results obtained during its prototype phase, as well as an update regarding the current status of the detector's deployment and long-term performance monitoring.