Rigify
Blender's built-in rig generator add-on
Also known as: Blender Rigify · Rigify rig · Meta-Rig · Blender auto rig · Rigify export Unreal
Definition
Rigify is a Blender add-on that generates a complete control rig from a simple template called a Meta-Rig. You fit the Meta-Rig to your character, press Generate, and Rigify builds a rig with IK and FK, spine and finger controls and a facial setup. It ships with Blender but is switched off by default, and must be enabled in Preferences > Add-ons. It saves hours compared with building a rig by hand.
In production
Rigify rigs are made for animation inside Blender, so exporting to a game engine needs care: export only the deform bones, because the control bones are not needed there, and check the bone names and hierarchy against what the engine expects. Weight the mesh to the generated rig with Automatic Weights and fix problems in Weight Paint Mode. Humanoid characters work best.