It's a perennial Helianthus or Sunflower. Many species, varieties and hydrids.
Commonest is Lemon Queen, yours looks like that one. The other common sunflower is Jerusalem Artichoke, Helianthus tuberosa, a surprisingly attractive border flower.

It seems too yellow and the petals rather longer for lemon queen but I agree it is a helianthus. how tall is it? there is one that gets 5ft + H. herbstonne.
they bare good garden plants.