Daniel Cassidy (1943-2008), an Irish-American writer, singer, filmmaker, and professor, was born in Brooklyn in 1943. He attended the the New York Military Academy on a musical scholarship, and studied English Literature and Creative Writing at Cornell University. His first job was at the New York Times, which he left to pursue screenwriting full time. From the late 1960s through the 1980s, Cassidy performed as a musician, but gradually transitioned into composing his own music. He performed at, among other places, Carnegie Hall, the LA Civic Auditorium, and on the Tonight Show. In addition to his musical work, Cassidy was also a prolific screenwriter--he sold film scripts and treatments, and worked in both film development and television production. His 1996 documentary, Civil Rights and Civil Wrongs, about the Troubles in Northern Ireland, was nominated for an Emmy Award, and his film Uncensored Voices aired on PBS.

In the 1990s, Cassidy's interests turned toward research and academia. Cassidy was a professor at New College of California, in the Media & Film Studies Department, where he taught storytelling, newspaper writing, and broadcast history classes. In 1995, he founded the Irish Studies Program (An Leann Eireannach) at New College. Cassidy was co-director of the program, one of the first in the country, until the college closed in 2008. Additionally, Cassidy was co-founder of the Crossroads Irish American Festival in San Francisco, and served as director of the festival until his death.

Cassidy was a prolific contributor to newspapers and journals. His book, How the Irish Invented Slang: The Secret Language of the Crossroads, was published in 2007. The book, which looked at the influence of Irish phrases on slang that developed in America in the 1800s, won the 2007 American Book Award for nonfiction. The book was met with much praise from within the Irish-American community, but was criticized by linguists for lacking evidence to support the book's claims. Cassidy's other research interest was African-American and Irish intermarriage in New York City in the 1800s, although he did not develop this enough before his death to publish any scholarly work on the topic. Cassidy died on October 11, 2008.