I can not be sure but I believe it is a sunflower.
I also note some yellowing (chlorosis) and stunting of lower leaves which may or may not be a sign of Downey Mildew, a common problem among Sunflowers. I am sending you some links with information on that and other common problems with Sunflowers.
More pictures - this mystery plant is growing like crazy. Maybe these pics will help in identifying.
Ok--those pictures are more helpful. It is Datura.
Oh no - just read about it - not good. My husband found three small potted plants near the parking lot at our church. We thought they were eggplants! Should I dig up and dispose of them? They are right up against my tomato plants. Please advise. Thank you.
My answer is yes! If in fact it is 'Datura' common name angels trumpet refers to two different plants Brugmansia and Datura. still they are poisonous and so growing near vegetables, (see link I've sent under Planting safely)