The Collaborative International Dictionary of English v.0.48:

Predecessor \Pred`e*ces"sor\ (?; 277), n. [L. praedecessor; prae
   before + decessor one who withdraws from the province he has
   governed, a retiring officer (with reference to his
   successor), a predecessor, fr. decedere: cf. F.
   pr['e]d['e]cesseur. See Decease.]
   One who precedes; one who has preceded another in any state,
   position, office, etc.; one whom another follows or comes
   after, in any office or position.
   [1913 Webster]

         A prince who was as watchful as his predecessor had
         been over the interests of the state.    --Prescott.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "predecessor":
   ancestor, ancestors, announcer, antecedent, antecedents,
   ascendants, avant-garde, bellwether, buccinator, bushwhacker,
   elders, explorer, fathers, forebear, forebears, forefather,
   forefathers, foregoer, forerunner, front runner, frontiersman,
   fugleman, grandfathers, grandparents, groundbreaker, guide,
   harbinger, herald, innovator, lead runner, leader, messenger,
   pathfinder, patriarchs, pioneer, point, precedent, precursor,
   predecessor, predecessors, progenitors, prototype, scout,
   stormy petrel, trailblazer, trailbreaker, vanguard, vaunt-courier,
   voortrekker