This dissertation aims to improve the theory of galaxy formation through two independent areas of investigation: 1) super-massive black hole (BH) scaling relations and 2) formation mechanisms of peculiar rings. Several scaling relations between BH masses and numerous properties of their host galaxies have been reported in the literature, implying a co-evolution scenario of galaxies and their central BHs. The first part of this dissertation explores these scaling relations in both observations and simulations. Chapter 2 presents two important applications of the scaling relations: a determination of black hole mass function (BHMF) and a search for intermediate-mass black holes (IMBHs). I estimated a local BHMF through imaging data only by using the statistically tightest correlations. This work provided a reliable census of local BHs, especially for the low-mass regime. This chapter then focuses on my contributions to a collaborative project in the search for IMBHs, in which I provided the BH mass estimations from the spiral arm morphology. This collaboration demonstrated, for the first time, the consistency between the predictions of several popular scaling relations in the low-mass regime. Chapter 3 explores the BH−galaxy connection beyond the bulge by using the Illustris simulation. This work showed Illustris establishes very tight correlations between the BH mass and large-scale properties of the host galaxy, not only for early-type galaxies but also late-type galaxies, regardless of bar morphology. These tight relations suggest that halo properties play an important role in determining those of the galaxy and its BH. The main focus of Chapters 4 and 5 is ring formation mechanisms, in particular the origin of Hoag-type galaxies. Studying such peculiar galaxies is important to address how different kinds of interactions contribute to different galaxy morphologies. Chapter 5 presents a photometric study of PGC 1000714, a galaxy with a fair resemblance to Hoag’s Object. This work has revealed, for the first time, an elliptical galaxy with two fairly round rings. A number of formation scenarios are discussed. However, there are many questions yet to address, especially the origin of the inner ring. This dissertation is just a beginning to understanding this interesting group of galaxies.