Improving Corporate Governance Through Diversity Act of 2021 This bill requires certain issuers of securities to disclose the racial, ethnic, and gender composition of their boards of directors and executive officers, as well as the status of any of those directors and officers as a veteran. It also requires the disclosure of any plan to promote racial, ethnic, and gender diversity among these groups. The Securities and Exchange Commission must establish a Diversity Advisory Group to report on strategies to increase gender, racial, and ethnic diversity among board members.