In the original version of the first Dark Tower novel, The Gunslinger, it was implied that the world of the Dark Tower series is a decayed future version of present-day Earth, thus the Great Old Ones are a future stage in the development of contemporary civilization.
The Power of Five are a series of five novels (2005-2013) by Anthony Horowitz in which 'the old ones' refers to a vague collection of demons (including half human and half animal mash-ups) attempting cross over through several "Gates" to enslave and torture the entire human race.