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Massive OB stars are rare and short lived. Yet they dominate the ultraviolet luminosities of star forming galaxies comma produce alpha elements comma and are mechanical energy powerhouses through their stellar winds and supernovae. OB stars are difficult to study and our knowledge of massive star populations is largely limited to the Milky Way and its nearby companions. We propose to use an efficient large-dither-mosaicking observing strategy to resolve and map OB star populations in 27 nearby galaxies within 7.5 Mpc by obtaining FUV and NUV images with the ACS-SBC and WFC3-UVIS on HST. GULP will observe galaxies covering a wide range of masses comma metallicities comma and star formation activity levels. GULP multi-wavelength data will capture large numbers of massive young stars in clusters comma OB associations comma and in field populations. GULP will provide a unique basis for calibrating modern massive star evolutionary models comma investigating the upper IMF and its dependence on metallicity and environment comma and understanding the role of stellar feedback in determining the evolution of starbursts and star-forming galaxies. GULP will allow us to link the properties of massive stars from their birth to their demise as supernovae. The project makes effective use of archival HST data comma adding unique UV photometry comma and allowing us to simultaneously investigate UV dust obscuration in a variety of galaxies. Results from GULP will thus provide a strong quantitative basis for quantifying the dust attenuation at FUV and NUV wavelengths comma indispensable for interpreting the rest-frame UV spectra of youthful galaxies with JWST.