Qutub-ud-din Aibak was the Sultan of Gulam dynasty. Many monuments were constructed by him, like Kubbat-ul-Islam mosque, Qutub Minar, Adhai din ka jhopda etc. According to the question Alai Darwaza was not constructed by Qutub-ud-din Aibak, it was constructed by Alauddin Khilji of khilji dynasty.