An object of the present invention is to provide a polarizer having a high degree of alignment and an image display device including the polarizer. The polarizer of the present invention is a polarizer which is formed of a polarizer-forming composition containing a polymer liquid crystal compound and a dichroic material, in which the polymer liquid crystal compound is a thermotropic liquid crystal and a crystalline polymer, the polymer liquid crystal compound and the dichroic material are horizontally aligned, and crystallinity of the polymer liquid crystal compound in the polarizer-forming composition is higher than the crystallinity of the polymer liquid crystal compound alone.