The Hawking–Page phase transition is named for Stephen Hawking and Don Page.
In their work on black holes in anti-de Sitter (AdS) space, Hawking and Page showed that an AdS black hole can coexist in thermal equilibrium with radiation without necessarily being the system’s preferred state. Below a critical temperature, thermal AdS dominates; above it, the large black-hole state becomes thermodynamically preferred.
The transition is significant because it links black-hole thermodynamics with phase-transition ideas from statistical physics. In the AdS/CFT correspondence, it is often interpreted as a confinement–deconfinement transition in the corresponding conformal field theory.
A common mix-up is Don Page’s separate work on black-hole information, including the Page curve. That later research made his name familiar in a different Hawking-related context, but the Hawking–Page transition specifically concerns AdS black-hole thermodynamics.