This invention relates a copolymer (D) containing (A) methacrylic polymer units each having, at an end thereof, at least one group represented by the below-described formula (1) and (B) units of an aromatic vinyl monomer, wherein a weight ratio (A:B) of the units (A) to the units (B) is A:B=5 to 95:95 to 5; and its use. The present invention can provide inter alia a copolymer useful as a pigment dispersant or the like capable of affording pigment dispersions useful for inkjet inks, colors for color filters, and other applications.