The Collaborative International Dictionary of English v.0.48:

Jerker \Jerk"er\, n.
   [1913 Webster]
   1. A beater. [Obs.] --Beau. & Fl.
      [1913 Webster]

   2. One who jerks or moves with a jerk.
      [1913 Webster]

   3. (Zool.) A North American river chub (Hybopsis
      biguttatus).
      [1913 Webster]

WordNet (r) 3.0 (2006):

jerker
    n 1: someone who gives a strong sudden pull [syn: yanker,
         jerker]