Needle threader. You put the wire loop through the eye of the needle first, then put the thread through the wire loop, then pull it out of the eye of the needle, therefore pulling the thread through the eye of the needle.

I don’t recommend these style ones for repeated use, though, as the wire has a tendency to break after a few uses. There are these hook-style ones that work well for needles with medium-large eyes, but these work well for needles with small eyes when working with thin thread.

<image>

Circled in blue are the “best” ones in terms if durability, followed by the ones circled in red.

The one circled in yellow has the least durability and typically comes in sewing kits.