Where does a quant trader fit into the picture?

If a quant researcher comes up with/tests ideas and models, and a quant developer is the one who implements the strategies into code, what does a quant trader actually do? I seem to hear that they're the ones executing or implementing the trades, but I don't really get how that's not what a quant dev is doing instead. I assume they're not manually pressing buy and sell so I don't really understand where they fit in.