it's a very healthy and robust pokeweed. think twice about pulling it. you'll need a shovel and a strong back. they have a taproot that goes forever. if the plant is in a wild area of your garden, leave it for the birds. personally, i think they're pretty cool.
just guessing -- at first I thought it might be elderberry, but the berries weren't right -- then I found "pokeweed" and I think that might be it -- do a search here at Dave's Garden for "pokeweed" and see what you think?
Or do like old folk at home, and make poke salad...the roots are poison, and to eat the leaves you have to boil them twice. If you leave it, there will be a million babies next year and that dern taproot comming back.