Devourers are a species of undead from the various worlds of Dungeons & Dragons. They resemble enormous undead humanoids with a gaping hollow in the center of their chest; devourers are soul-eaters, and when a devourer has a soul imprisoned in its unearthly gullet, a tiny and tortured effigy of their victim appears inside the hollow in their chest, acting like a prisoner held in a cage. The first devourers appeared as a result of people dying on the Astral Plane and then somehow reviving, but they have since spread across the planes; Orcus finds them particularly appealing.
They then made it into Dungeons & Dragons 4th Edition, once more appearing in the Monster Manual. This edition divided the Devourer into three different versions; the original devourer was now renamed the Spirit Devourer, to contrast the Viscera Devourer (actually a conversion of the Mohrg), and a new, more powerful devourer called the Soulspike Devourer, which has giant ribcage spears it can impale multiple souls on until it's ready to eat them.
In Dungeons & Dragons 5th Edition, though, they didn't appear until Volo's Guide to Monsters.