Active galactic nuclei (AGN) are the central engines hosted by most of the galaxies in the universe and are believed to be actively accreting supermassive black holes. The growth of the central black hole is very closely tied with the host galaxy evolution, as demonstrated by relations like the M-sigma relation. AGNs strongly influence galactic evolution by affecting star formation, as well as impacting their large-scale environment consisting of clusters, groups, and voids, via various feedback mechanisms. In addition, AGNs allow us to understand black hole physics and the evolution of supermassive black holes through the accretion processes. For my PhD research, I have attempted to understand the evolution of AGN and the role that the interplay between AGNs and the large-scale environment plays in their evolution, and have worked on the detection of galaxy clusters. For the first part of my dissertation, I have presented our investigation of the abundance of AGNs in galaxy clusters and the surrounding low-density fields using multi-wavelength surveys. We have found a decreasing fraction of AGN with increasingly denser environments - (2.37+-0.39)% in clusters and (5.12+-0.16)% in fields. This shows an environmental dependence of AGN activity. For the second part, I have presented our study of the abundance of AGNs in cosmic voids. We have found higher average fractions in the inner voids (4.9+-0.7)% than in the outer void regions (3.1+-0.1)% at z>0.42. At low redshifts (z<0.42), we have found very weak AGN activity dependence on the environment. The third part of the dissertation has detailed a multi-wavelength study of a changing look blazar, B2 1420+32. We have discovered a multi-transitional changing look blazar with unprecedented photometric and spectroscopic variabilities and complex spectral features. Multi-epoch lightcurves spectra have shown very large gamma-ray and optical variability, by factors of up to 40 and 15, respectively, on week to month timescales.
Over a 15-year period, the gamma-ray and optical fluxes have been observed to increase by factors of 1500 and 100, respectively. Most emission line flux variations, except the Fe continuum, have been seen to be within a factor of 2-3, implying that the transitions between FSRQ and BL Lac classifications are mainly caused by the continuum variability. Finally, in the last part of the dissertation, I have presented the initial analysis for the detection of X-ray selected galaxy clusters using the SWIFT Observatory data as part of the Swift AGN and Cluster Survey (SACS) sequence.