Born in Aberdeen, Scotland, Alexander Milne Calder made Pennsylvania his home in 1868 and earned the commission to create the decorative sculptural program for the City Hall of Philadelphia. This project consumed much of his career, and while supervising it, he oversaw a small army of artisans and workmen who used Old World skills in the "tremendous decorative sculptural program" (Baigell 58)

One of his best-known works is likely the huge statue of William Penn on top of the City Hall in Philadelphia. With naturalistic likeness, it is based on Benjamin West's depiction of the state's founder and is 36 feet tall and weighs 26 tons. This project was the main focus of Calder's professional life between 1886 and 1892, and his biggest challenge was finding a foundry that could handle such a large work. He also sculpted the equestrian statue of General George Gordon Meade, which was installed in 1881 in Fairmount Park in Philadelphia.

His son, Alexander Stirling Calder, and grandson, Alexander Calder, appear to have inherited his talent.

Sources include:
Matthew Baigell, Dictionary of American Art
Georg Sheets, Pennsylvania Heritage