Every massive galaxy is thought to harbor a supermassive black hole at its center, but the processes by which these black holes are formed and grow to supermassive scales are not fully understood. Semi-analytic modeling offers a way to explain observed luminosity functions and empirical relations using simple physical prescriptions for black hole evolution. We find that luminosity functions for z>2 are explainable assuming only the Eddington limit, merger-triggered accretion, and a connection between black hole mass and gas supply. In addition, signatures of black hole seeding may be present in a number of observables--particularly high-redshift luminosity functions and gravitational waves--but these signatures are degenerate with uncertainties regarding either black hole accretion and dynamics. Finally, I assess the capability for black holes to explain unknown excesses in the cosmic infrared background.