In relativistic heavy-ion collisions, a quark-gluon plasma (QGP) is formed. Governed by Quantum Chromodynamics, the QGP emerges as a fundamental aspect of the Standard Model of particle physics and has likely existed in the earliest instants of our universe. Phenomenological investigations reveal a rapid transition of the plasma into a nearly-perfect fluid within mere yoctoseconds, showcasing its intriguing behavior. The pre-equilibrium evolution of the QGP, leading to this fluid-like state, encompasses a rich variety of phenomena important for interpreting heavy-ion collision data. In this colloquium, we delve into some of the less understood aspects of the pre-equilibrium QGP dynamics. Specifically, we explore nonperturbative collective excitations, universal dynamics, and innovative strategies aimed at deciphering the initial stages using experimental probes such as jets and heavy quarks. Through these discussions, we aim to shed light on the fundamental properties of the QGP and its implications for high-energy physics.