This thesis presents an experimental study at local scale of the 1T-TiSe2 surface with scanning tunneling microscopy and spectroscopy (STM/STS). This quasi two dimensional layered crystal is particularly interesting for solid state physics due to its phase transition to a 2x2x2 commensurate charge density wave (CDW) accompanied by a weak periodic lattice distortion (PLD) below 200 K. In a first step, the main native atomic defects are precisely identified and characterized. Their structural and electronic properties are studied in detail at low temperature, in the presence of the CDW. The work then focuses on one defect type (i.e., intercalated Ti) having a dramatic influence on the CDW order parameter. In particular, it is shown that increasing the density of intercalated Ti atoms in the van der Waals gap of 1T-TiSe2 induces a gradual loss of the long range phase coherence of the CDW, which starts to build phase-shifted, but commensurate, nanodomains. In addition, the resilient character of the CDW related to the intrinsic presence of two different PLD-induced conformations of intercalated Ti, is revealed, demonstrating the presence of a mutual CDW-defect interaction mechanism. Finally, a newly discovered defect in an intentionally Ti-doped 1T-TiSe2 crystal is used to intimately probe the PLD by the STM technique.