We introduce the concept of magnet-free nonreciprocal graphene components at terahertz (THz) frequencies based on spatiotemporal modulation of graphene conductivity. As an example, we design a fully planar, reconfigurable, plasmonic isolator using a graphene parallel-plate waveguide with timevarying gate voltages that implement the required travellingwave-like perturbation. We envision that this approach will lead to reconfigurable non-reciprocal THz components with unprecedented performance and functionalities, with applications in biosensing, communications, imaging, and detecting devices.