So I know that literally a math equation. Mean his literally sentient Math.
Any their name is DKTZY RRR

And very smart smallpox virus

Yes you do little man. Yes you do
And Yellow lantern who is a virus who's name is Despotellis

And another one who is literally corps because for some reason his ring won't accept his death
Driq everyone

Fun Fact: All lantern have oaths recharge their ring this the oranges oaths
"What's mine is mine and mine and mine. And mine, and mine, and mine! Not yours!"
There's another one that actually sounds like a oath but I found this one funny
So you asking how they become Green Lantern? Is because with enough will power anything can become a Lantern. And I Mean ANYTHING! So here my question if will can be lantern enough termination and will? Can sperm be a green lantern?