The Hamm hologram (or holohamm) was created with tech from 8i, a company focused on creating "volumetric" videos of real people -- essentially, 3D captures of humans that you, as a viewer, can walk all around.
The holohamm was created for the premiere party of the film "Marjorie Prime" at the Sundance Film Festival. In the movie, the "Mad Men" actor actually plays a hologram, an artificially intelligent simulation of an elderly character's deceased husband designed to keep her company.
See the full story here: https://www.cnet.com/au/news/jon-hamm-hologram-marjorie-prime-holohamm-sundance-mixed-augmented-reality/