  H\"{o}lder's inequality, since its appearance in 1888, has played a
fundamental role in Mathematical Analysis and it is, without any doubt, one of
the milestones in Mathematics. It may seem strange that, nowadays, it keeps
resurfacing and bringing new insights to the mathematical community. In this
expository article we show how a variant of H\"{o}lder's inequality (although
well-known in PDEs) was essentially overlooked in Functional Analysis and has
had a crucial (and in some sense unexpected) influence in very recent and major
breakthroughs in Mathematics. Some of these recent advances appeared in
2012-2014 and include the theory of Dirichlet series, the famous Bohr radius
problem, certain classical inequalities (such as Bohnenblust--Hille or
Hardy--Littlewood), or even Mathematical Physics.
