Drivers are people in Xenoblade Chronicles 2 and Xenoblade Chronicles 2: Torna ~ The Golden Country who have awakened Blades.
Drivers are not visibly different from any other person. It is a hidden property of everyone, best described as an "aptitude", as to whether they can become a Driver or not. The only way to know is to try; a potential Driver must attempt to resonate with a Blade's Core Crystal to discover whether they can. If they can, the Blade within the crystal takes shape. If they cannot, they are overcome by the crystal's energies and suffer injuries, ranging from nosebleeds to fainting. A Driver can bond with a large amount of Blades at once.
Drivers and Blades fight alongside each other. The Driver performs most attacks, and occasionally passes the weapon to the Blade so they can use powerful special attacks. As Blades generally do not take lasing damage, the Driver is the focus of all enemy attacks. If the Driver dies, the Blade reverts to its Core Crystal form, and remains inert for a time before a new Driver can awaken it. In order for a Driver and Blade to fight effectively, they must channel ether from the weapon to the Blade and back to the Driver. If this link is disrupted or broken, the weapon becomes inert of elemental powers. It is shown possible for a Driver to use a Blade's powers directly if they choose to impale themselves with the weapon, allowing them to channel ether directly from the weapon into themselves, which is not recommended.
Being a Driver is not limited to humans or human-adjacent species. Nopon can be Drivers, Blades can be Drivers of other Blades, and even monsters can become Drivers under the right circumstances.
In Torna ~ The Golden Country, it is revealed that the strategy of a Driver sharing the Blade's weapon between them both is a relatively recent invention. Prior to this, it was normal for a Driver to fight only with their own mundane weapon. The idea of sharing a Blade's weapon was created by Lora and Jin, mostly because they only had one weapon between them. Addam became intrigued by the idea, and from there it spread to become the standard.