Resist composition, method for forming resist pattern, compound, and polymer compound

In the present invention, there is employed a resist composition having, as a base resin, a polymer compound that has constituent units derived from a compound expressed by general formula (a0-m). In the formula, W is a polymerizable-group-containing group; RAr1 and RAr2 are aromatic groups; R01 and R2 are iodinated alkyl groups, iodine atoms, or hydrogen atoms; L11 to L15 are linking groups; q is 0 or 1; when q is 0, R02 is an iodinated alkyl group or an iodine atom, and j2 is an integer of 1 to 5; when q is 1, one or more iodine atoms are included in both R01 and R02; and k1 and k2 are each 0 or 1. When q is 0, k2 is 1; when q is 1, k1 + k2 is equal to 1. Mm+ is an m-valent onium cation. This resist composition yields higher sensitivity during formation of a resist pattern and makes it possible to form a pattern having improved lithographic characteristics such as reduction in roughness.