The Atacama Cosmology Telescope (ACT) is a dedicated 6-meter telescope that observes the sky in three bands at 148 GHz (2 mm), 218 GHz (1.4 mm), and 277 GHz (1.1 mm). ACT completed its first phase of observations in late 2010, after being pointed to the sky for the first time in 2007. These observations have already yielded numerous scientific results across a range of astrophysical subjects. In particular, ACT has enabled the discovery of galaxy clusters by means of the Sunyaev-Zel'dovich Effect (SZE), which is a distortion on the CMB spectrum caused by the hot intracluster gas. Since the SZE is essentially redshift-independent, a sample of clusters like the one found by ACT can be a crucial probe of cosmology. We are carrying an extensive multi-wavelength follow-up campaign, with a large fraction of it being observed from Gemini, that will help us characterize and understand the complex physics within clusters and their evolution with time and, ultimately, the formation of structure in the Universe. Here, we review our current results which include cluster detection, dynamical masses and an introduction to our multi-wavelength effort through the case of the most remarkable SZE-selected cluster yet found, "El Gordo".