Bimetallic catalysts, methods of producing bimetallic catalysts comprising a modified Ziegler-Natta catalyst and a metallocene, and methods of olefin polymerization using such catalysts are provided. The method of producing the bimetallic catalyst may include combining (a) a Ziegler-Natta catalyst comprising a Group 4, 5 or 6 metal halide and/or oxide, optionally including a magnesium compound, with (b) a modifier compound (“modifier”), wherein the modifier compound is a Group 13 alkyl compound, to form a modified Ziegler-Natta catalyst. The modified Ziegler-Natta catalyst is preferably non-activated, that is, it is unreactive towards olefin polymerization alone. The molar ratio of the Group 13 metal (of the modifier) to the Group 4, 5 or 6 metal halide and/or oxide may be less than 10:1. The bimetallic catalysts are useful in producing bimodal polymers, particularly bimodal polyethylene, having a Polydispersity (Mw/Mn) of from 12 to 50, which may be used in pipes and films.