The statement "Liquid Architecture is an architecture, whose form is contingent on the interest of the beholder" was made by Greg Lynn, a prominent architect known for his work in the field of digital and parametric design.
Greg Lynn’s concept of "Liquid Architecture" explores the idea that architecture can be dynamic and responsive, changing in form based on the interaction with its users or the environment. This contrasts with traditional static forms.
Marcos Novak, Peter Eisenmann, and Bernard Tschumi have also made significant contributions to architectural theory, but this specific idea is attributed to Greg Lynn.