1. May 4, 1886 marked the start of the infamous Haymarket Riot in Chicago, which had a significant impact on the labor movement in Wisconsin. The incident happened during a labor demonstration for an eight-hour workday when a bomb exploded, killing police officers and civilians. The riot led to the suppression of labor rights and caused heightened concerns about anarchism and socialism.

2. May 4, 1929, is the birthdate of Audrey Hepburn, one of the most beloved actresses of all time. Although she was not born in Wisconsin, she spent several years in the state while attending boarding school at The Spence School in the late 1930s.

3. May 4, 1970, was the day when anti-war protests on the campus of Kent State University turned deadly. National Guardsmen opened fire on a crowd of unarmed students, resulting in four deaths and nine injuries. The incident sparked protests across the country, including in Wisconsin, where demonstrations took place at a number of universities.

4. May 4, 1994, saw the opening of the Milwaukee County Zoo's new Primates of the World exhibit. The exhibit features over 200 primates from around the globe, including gorillas, orangutans, and lemurs. The zoo remains one of the state's most popular tourist destinations.

5. May 4, 2006, is the date when the state's comprehensive smoking ban took effect. The law prohibits smoking in all public places and workplaces, including bars and restaurants. The ban has been credited with improving air quality, reducing healthcare costs, and encouraging more smokers to quit.