The existence of Non-Fermi liquids which are not described by Landau's Fermi liquids is a fascinating puzzle in theoretical physics. In this talk, I will show universal field theories where we can go around the Landau's Fermi-liquids and obtain Non-Fermi-Liquid behavior. These field theories contain dynamical singlet fermions which couple through fermion bilinear terms to strongly coupled sectors which are characterized by its ``dynamical scaling''. Suppose these strongly coupled sectors have gravity dual (which is not necessarily anti-de Sitter space), then by using powerful gauge/gravity duality, I will argue how these dynamical scaling parameters determine the natures of the dynamical singlet fermions in a very universal way; These natures include the existence of Fermi-/Non-Fermi liquids, sharp Fermi-surface, the decay rates and breakdown of the quasi-particles description. I will end with discussion for generalization of our work to include the lattice effects and impurities for more interesting condensed matter system.