The Langton's ant is studied from the point of view of topological dynamical systems. A new approach which associate a subshift to the system is proposed. The transition rule is generalized to the family of bi-regular graphs Γ(k,d) and the dependence of the dynamical system on k and d is analyzed. A classification of the Γ(k,d) graphs based on the dynamical properties of the subshift is established. Also a hierarchy is defined on the graphs through the subset relation of the respective subshifts. The analysis are worked out by establishing an algebraic characterization of the forbidden words of the subshift.