In this paper we give a complete classification of all Painlevé‐type hyperbolic partial differential equations (PDE's) over the complex domain of the form uxy = F(x, y, u, ux, uy where F is rational in u, ux, and uy, and locally analytic in x and y. We find exactly 22 equivalence classes of equations (under coordinate changes and Mobius transformations in u), which we denote HS‐I, HS‐II,…, HS‐XXII. A canonical representative of each class is presented and solved by transforming it either to a well‐known soliton equation (sine‐Gordon, Bullough‐Dodd‐Mikhailov) or to a linear equation by means of a Bäcklund correspondence or simpler change of variables. (The parabolic case, in which 10 more canonical equations are obtained, and semilinear PDE's in three or more variables are treated in the accompanying paper II.) The proof that the list is complete involves investigating four sets of necessary conditions in turn, each of which has essentially new features peculiar to the PDE context, as well as familiar features analogous to the corresponding conditions for ordinary differential equations (ODE's) as discussed in the classical literature by Painleve, Gambier, Ince, Bureau, and others. In a setting sufficiently general to embrace ODE's, hyperbolic and parabolic PDE's, and higher dimensional semilinear PDE's, we classify 76 types of O/PDE's, denoted DE‐1,…, according to their Bureau symbols and resonance data, which satisfy those necessary conditions for the Painlevé property common to each of these four Painlevé classification problems.