We present a comprehensive study of the spectrum of the narrow-line Seyfert 1 (NLS1) galaxy RE J1034]396, summarizing the information obtained from the optical to X-rays with observations from the William Herschel 4.2 m Telescope, the Hubble Space T elescope, the Extreme Ultraviolet Explorer, ROSAT , ASCA, and BeppoSAX. The BeppoSAX spectra reveal a soft component which is well represented by two blackbodies with and 160 eV, mimicking that expected from a hot, optically kT eff \ 60 thick accretion disk around a low-mass black hole. This is borne out by our modeling of the opticalÈtoÈ X-ray nuclear continuum, which constrains the physical parameters of a NLS1 for the Ðrst time. The models demonstrate that RE J1034]396 is likely to be a system with a nearly edge-on accretion disk (60¡È75¡ from the disk axis), accreting at nearly Eddington rates onto a low-mass black (0.3È0.7L Edd ) hole This is consistent with the hypothesis that NLS1s are Seyfert-scale ana-. logies of galactic black hole candidates. The unusually high temperature of the big blue bump reveals a Ñat power-lawÈlike continuum in the optical/UV which is consistent with an extrapolation to the hard X-ray power law, and which we speculate may be similar to the continuum component observed in BL Lac objects in their quiescent periods. From the BeppoSAX and ASCA data, we Ðnd that the slope of the hard X-ray power law depends very much on the form of the soft component which is assumed. For our best-Ðtting models, it lies somewhere between a \ 0.7 and 1.3 and thus may not be signiÐcantly softer than active galactic nuclei in general.