The Hagedorn temperature is a source of continuing fascination and insight into thermal physics of both string theory and gauge theory. The deeper reason for this shared feature is now seen as a consequence of the duality between gauge and string theories, as made precise by the AdS/CFT correspondence. Amazingly, integrability symmetry gives access to the Hagedorn temperature of N=4 SYM at strong coupling regime by a numerical calculation, allowing a direct match to the string theory side of the correspondence. This connects to recent progress that the Hagedorn temperature can be computed as a winding mode along a thermal circle. We propose a curvature-corrected thermal scalar equation of motion, which captures corrections to the Hagedorn temperature on curved backgrounds. This is tested on pp-wave and AdS backgrounds.