Gordon Freeman is the theoretical physicist protagonist of the Half-Life series. His silence is a deliberate design choice by Valve to allow players to project themselves onto the character, making the immersive experience of the Black Mesa Incident and the resistance against the Combine more personal.

The G-Man is an enigmatic interdimensional bureaucrat who wields immense power over time and space. While his employers and ultimate motives remain unknown, he orchestrates key events in the Half-Life universe, 'nudging' individuals like Gordon Freeman to alter the course of history.

The Resonance Cascade was a catastrophic event triggered when Gordon Freeman inserted a specific Xen crystal sample into the Anti-Mass Spectrometer. This tore a rift between Earth and the border world Xen, allowing alien wildlife to invade the facility and eventually leading to the Combine's attention.

The Combine (or Universal Union) is a vast, multidimensional empire that conquers and assimilates universes. They invaded Earth to strip it of its resources, particularly its ability to teleport, after detecting the portal storms caused by the Resonance Cascade and the death of the Nihilanth.

Half-Life and Portal share the same universe. Aperture Science (Portal) and Black Mesa (Half-Life) were rival research corporations. The Borealis, an Aperture Science research vessel mentioned in Half-Life 2: Episode Two, contains technology that both the Resistance and the Combine are desperate to secure.

Half-Life 3 is one of the most famous unreleased games in history. While Valve has not officially confirmed its development, the release of 'Half-Life: Alyx' in 2020 reignited hope, as its ending significantly altered the timeline and set the stage for a potential continuation of Gordon Freeman's story.

Headcrabs are parasitic alien creatures from Xen. They leap onto a host's head, burrowing in and taking control of the nervous system, mutating the host into a mindless, aggressive 'zombie.' They come in several varieties, including standard, fast, and poisonous types.

The Zero Point Energy Field Manipulator, or Gravity Gun, revolutionized FPS gameplay by allowing players to pick up, throw, and manipulate heavy objects. It turned the physics engine into a weapon and puzzle-solving tool, becoming one of the most iconic weapons in gaming history.

Alyx Vance is a key figure in the human resistance and Gordon Freeman's primary companion. Daughter of scientist Eli Vance, she is a skilled hacker and fighter. Her survival and actions are crucial to the resistance's success, and she becomes the central focus of the VR title 'Half-Life: Alyx'.

The Seven Hour War was a brief conflict where the Combine empire invaded Earth and defeated all human armed forces in just seven hours. It resulted in humanity's surrender, negotiated by Dr. Wallace Breen, who was then appointed as the administrator of Earth under Combine rule.