Who propounded Kashmir Shaivism?

Kashmir Shaivism (the Trika system) was propounded by Vasugupta in the early 9th century CE. He is credited with revealing the Shiva Sutras, the foundational text of the Trika/Pratyabhijna school of non-dual Shaivism. Abhinavagupta later expanded and systematised the philosophy, but its original propounder was Vasugupta.