Flowey is the first character you can find in Underscratch.
He is a Golden Flower. In a friendly way, he`ll greet you to the basics of the game (Buggy, watch out). If you hit the bullets he`ll call you a IDIOT, and attempts to kill the protagonist in the start of the game, but fails, since Toriel goes into the rescue.
At the end, he`ll absorb the human souls and become a horrifying beast named "Omega Flowey"