An entirely new perspective on the Universe emerged with humanity’s first observations of gravitational waves a decade ago. These messengers of gravity are ripples in the fabric of spacetime launched from the extreme environments of colliding black holes and detected on Earth for the first time in 2015 by the Laser Interferometer Gravitational Wave Observatory (LIGO). Over the past decade astronomers have used this gravitational messenger, along with traditional astronomical observations of light, to uncover many long-held secrets in physics and astronomy. We have, however, only just begun to learn about our Universe from this new discipline of multi-messenger astronomy. In only the last few years we have begun to break open a new realm of gravitational wave observations from merging black holes that are up to billions of times larger than the merging black holes detected by LIGO. These supermassive black holes probe different physical regimes and stand to again open the flood gates of discovery. This research program will build-up necessary theoretical frameworks needed to describe the astrophysical processes which generate multi-messenger signatures from these monstrous black hole mergers. The aim is to predict observational signatures of these supermassive black hole binaries interacting with their environments. To do so the program will pioneer new models of these interactions to facilitate their discovery and interpretation. In this way the program will advance the state