There is disclosed a catalyst composition for the polymerization of olefins, particularly alpha-olefins. The composition is prepared by synthesizing a catalyst precursor and then combining it with a conventional catalyst activator. The precursor is synthesized by: (a) contacting a solid, porous carrier with an aluminum compound; (b) contacting the resulting product with a mixture of vanadium and titanium compounds; (c) contacting the product with an alkyl ether and (d) pre-activating the product of step (c) with a mixture of a halogenating agent and an aluminum compound.The catalyst composition is used without a halogenating agent in the polymerization medium to produce narrow molecular weight distribution HDPE and LLDPE products, or with a halogenating agent in the polymerization medium to produce broad molecular weight distribution LLDPE and HDPE products.