Proteus, with a mean radius of 209 ± 8 km, is the largest irregular-shaped icy body in the Solar System. It has a primitive, heavily cratered surface. Its most prominent feature is an impact crater μ255 km in diameter and 10- to 15-km deep, relatively one of the largest craters in the Solar System. This prominent crater is similar in relative size to giant impacts on several other planets and satellites, all of which are larger than a recent theoretical limit for catastrophic disruption. Consistency is obtained by inclusion of reaccumulation in the disruption analysis. Based on this reanalysis, Proteus was not brought "to the brink" of catastrophic destruction by the giant impact, but only to the limit beyond which the surface of the impacted body and the form of the disrupting crater are modified beyond recognition. A network of large streaks, interpreted as troughs, are also discernable. This network, too extensive to be explained by strains produced in traditional thermal history calculations, may represent the onset of significant internal disruption in near-catastrophic impacts. Proteus' sphericity is near unity, but it has one of the roughest surfaces known. Thus Proteus is a transitional object in the irregular-spherical shape spectrum for icy satellites: its global figure is relaxed, but its surface features are unrelaxed. Proteus' intermediate relaxation state requires relatively high internal temperatures. The required temperatures and the observed radius of the shape transition for icy bodies is consistent with radiogenic heating in bodies with deep porous regoliths.