Extreme black holes possess event horizons at zero temperature, referred to as degenerate Killing horizons. These horizons are exclusively delineated by a specific limiting procedure, defining a near-horizon geometry or, more broadly, a quasi-Einstein equation which governs their properties. Solutions to this equation manifest as triples (M, g, X), where M represents a closed manifold (the horizon), g denotes a Riemannian metric, and X is a 1-form. The talk will be a overview of these concepts and relevant results which characterize solutions to the quasi-Einstein equation. This is joint work with Eric Bahuaud, Hari Kunduri, and Eric Woolgar.