William Jacob Aldag (30 November 1905 – 10 November 1974) was an Australian rules footballer who played for Footscray and Collingwood in the Victorian Football League (VFL). Aldag had his first league season in 1928 with Footscray. In 1930, he joined Collingwood and was a half-forward flanker in their record-setting 1930 premiership team.