Given the consequences and global significance of El Niño-Southern Oscillation (ENSO) events it is essential to understand the representation of El Niño diversity in climate models for the present day and the future. In recent decades, El Niño events have occurred more frequently in the central Pacific (CP). Eastern Pacific (EP) El Niño events have increased in intensity. However, the processes and future implications of these observed changes in El Niño are not well understood. Here, the frequency and intensity of El Niño events are assessed in models from the Coupled Model Intercomparison Project phases 5 and 6 (CMIP5 & CMIP6), and results are compared to extended instrumental and multi-century palaeoclimate records. Future changes of El Niño are stronger for CP events than for EP events and differ between models. Models with a projected La Niña-like mean state warming pattern show a tendency towards more EP, but fewer CP events, compared to models with an El Niño-like warming pattern. Among the models with more El Niño-like warming, differences in future El Niño can be partially explained by Pacific decadal variability (PDV). During positive PDV phases, more El Niño events occur, so future frequency changes are mainly determined by projected changes during positive PDV phases. Similarly, the intensity of El Niño is strongest during positive PDV phases. Future changes to El Niño may thus depend on both mean state warming and decadal scale natural variability.