An attractive feature of Grand Unified Theories (GUTs) is that all three fundamental interactions of the Standard Model (SM) originate from a single interaction at a high energy scale. Accordingly, the SM quarks and leptons are also unified by GUT symmetry which leads to a prediction of proton decay as well as the quantization of their electric charges. At the frontiers of high energy physics and cosmology, including that of the GUTs, there are 5 fundamental questions. What drives primordial inflation? What is the nature of dark matter? Why are neutrino masses extremely tiny? Where does the ordinary (baryonic) matter come from and what happened to the antimatter? Why is CP violation negligible for strong nuclear interactions? We will present two scenarios based on two popular GUT frameworks, SO(10) and SU(5), which can address the outstanding issues discussed above.