Cosmo Hamilton, born Henry Charles Hamilton Gibbs, was an English playwright and novelist. He was the brother of writers Arthur Hamilton Gibbs, Francis William Hamilton Gibbs, Helen Katherine Hamilton Gibbs and Sir Philip Gibbs.

Sir Philip Armand Hamilton Gibbs KBE was an English journalist and prolific author of books who served as one of five official British reporters during the First World War. Four of his siblings were also writers, A. Hamilton Gibbs, Francis Hamilton Gibbs, Helen Hamilton Gibbs, and Cosmo Hamilton, as was his father Henry James Gibbs, and his own son, Anthony.