Frank O'Hara
https://www.poetryfoundation.org/poets/frank-ohara
Poetry Foundation provides an excellent biography of O'Hara, in addition to a vast selection of his poetry and collections that place O'Hara's work in context with other poets of time.
Billie Holiday
https://www.biography.com/people/billie-holiday-9341902
A brief biography of Billie Holiday, which covers her early life, the development of her music career, and her tragic death.
Frank O'Hara's Lunch Poems: 21st-Century Poetry written in 1964
An article in The Atlantic which draws parallels between the style and essence of O'Hara's work and contemporary life.
Manhattan in Frank O'Hara's "The Day Lady Died"
http://booma.us/manhattan-frank-oharas-day-lady-died/
This article explores the geography of "The Day Lady Died."
On "The Day Lady Died"
http://www.english.illinois.edu/maps/poets/m_r/ohara/ladydied.htm
The article compiles the comments various writers, artists, and critics made about "The Day Lady Died."
The Ongoing Influence of Frank O'Hara, the Art World's Favorite Poet
https://www.artsy.net/article/artsy-editorial-ongoing-influence-frank-ohara-art-worlds-favorite-poet
An article on Artsy that describes O'Hara's enduring cultural relevance in contemporary art and poetry.