A JWST snapshot into the nature, diversity, and evolutionary pathways of the first galaxies

The emergence of the first sources ~13.5 billion years ago had a profound effect on the Universe, initiating its last major phase-change (the "Reionization process") and ending the so-called cosmic Dark Ages. Unlocking the physics of those primordial sources thus represents a fundamental step towards a comprehensive understanding of the aftermath of the Big Bang, and how the first objects and dark matter halos formed the building blocks for the Universe we see today. Despite progress, however, little is known about their underlying properties and evolution over the first billion years: When and how did the first sources form? What did their chemical enrichment journeys look like? Did they have supermassive black holes and what were their seeds? Did they ionize the Universe? The Hubble and Spitzer Space Telescopes provided us with a tantalising yet limited glimpse into these questions. The arrival of the revolutionary James Webb Space Telescope has now opened an unprecedented window in the early Universe, revealing one that is far more spectacular, diverse, and unpredictable than previously thought. In this talk I will summarize how Hubble and Spitzer set the foundations for our understanding of the high-redshift Universe, how the newfound photometric and spectroscopic capabilities of JWST are rewriting the textbooks on early galaxy formation, and how the first instances of galaxy formation look completely unlike the Universe we see today, through the discovery of galaxies out to unprecedented redshifts, with anomalous chemical abundances, vast ionized bubbles, and an abundance of (overly-)massive black holes.