The co-founder of the first women's labor union in the U.S. is Kate Mullaney. Established in 1850, the union aimed to improve working conditions and promote the rights of female workers, particularly in the garment industry. Mullaney's leadership and advocacy skills played a critical role in mobilizing women around labor rights issues. She organized strikes and negotiations, highlighting the challenges faced by women in the workforce. This groundbreaking initiative paved the way for future labor movements and set a precedent for women's roles in organized labor, championing equality and justice in the workplace.