King In Black was a major crossover event that took over Marvel Entertainment. The premise saw Knull, the Symbiote god, descend on the known universe. With Earth-616 in his crosshairs, he took over the planet in a way that no other villain had managed before.
The MCU has slowly started to play with the idea of impending Symbiotes, especially with the Venom crossover. Considering Phase 5 will surely feature further deities, it’s plausible that Knull is soon introduced; his weapon has already been seen in the hands of Gorr the God Butcher.