This doctoral dissertation discuss the main properties of the host galaxies of those active galactic nuclei (AGN) capable of generating strong relativistic jets (and therefore, capable of emitting up to the γ−ray energy ranges) and with their jets pointing very close to the line of sight, namely; blazars (including flat spectrum radio quasars [FSRQ] and BL Lac objects [BL Lac]) and narrow-line Seyfert 1 galaxies (NLSy1s). Our aim is to identify galaxy properties that might influence its AGN and vice versa. Despite the progress on AGN research and important results such as the correlation found between the spheroid (elliptical galaxies or bulges in disc galaxies) properties and its central super massive black hole mass (which suggests a link between evolutionary processes of the galaxy and its black hole and hence, a likely relation between the host galaxy and its AGN) the relation between the jet that some AGN are capable to launch and its black hole remains unclear, although it is essential for the understanding of the energy release mechanisms and AGN evolution. Motivated by this, in this thesis work I take advantage of Nordical Optical Telescope (NOT) near infrared (nir) imagery and perform a homogeneous and systematic structural modeling of a sample of radio–loud AGN with prominent relativistic jets and redshifts 0.3 < z < 1.0 and also, compile host galaxy and nuclear magnitudes for radio–loud AGN from literature. The combined sample (our analysis and the compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities L1.4GHz ∼ 1023.7 − 1023.7W Hz−1 , allowing us to divide our blazars sample into high-luminosity blazars (HLBs) and low-luminosity blazars (LLBs). The main results of this part of the thesis was published in Olguin-Iglesias et al. (2016) where We found that the host galaxies of our sample are bright and seem to follow the µe − Reff relation for ellipticals and bulges (Kormendy relation). The two populations of blazars show different behaviors in the Mnuc −Mbulge plane, a statistically significant correlation is observed for HLBs and a constant Mbulge for the whole range of Mnuc of LLB. As shown by previous studies, we find that both blazar types are hosted by massive red elliptical galaxies; the so called, jet paradigm.