Thomas Keightley (1789–1872) was an Irish writer who made significant contributions to the study of mythology and folklore. He is recognized as an early pioneer in the academic field of folklore, employing a comparative method that analyzed parallels between tales and traditions across different cultures. Keightley was cautious in his conclusions, acknowledging that similarities might arise from independent invention rather than direct transmission. His seminal work, 'Fairy Mythology' (1828), explored the origins and connections of fairy lore, drawing from various European traditions and earning praise from scholars like Jacob Grimm. The book underwent several editions and was later reissued under different titles, demonstrating its enduring influence. Beyond folklore, Keightley also authored numerous historical textbooks for educational institutions, including those adopted by Rugby School. He possessed a broad linguistic knowledge, enabling him to translate and digest various medieval and foreign works, further enriching his scholarly output.

Keightley stands out as an important early figure in comparative folklore collection. His most influential work, 'Fairy Mythology' (1828), was groundbreaking for its time, setting high standards for the study of folklore. He adopted an approach similar to the Brothers Grimm, investigating the connections between national myths and the religious and mythological systems of other regions. Initially, Keightley sought to trace fairy myths to Germanic and Teutonic roots, but he eventually concluded that tracing myths to a single ultimate source was unlikely. Instead, he proposed that similar myths could arise independently, stemming from shared human experiences and a fundamental uniformity in human nature, an idea influenced by Enlightenment thought. The book was well-received, praised by Jacob Grimm, and saw multiple reprints and expanded editions, reflecting its lasting impact and Keightley's own hopes for its immortality.

Beyond his work in folklore, Keightley was a prolific author of historical texts designed for educational purposes. At the request of educator Thomas Arnold, he produced a series of history textbooks covering English, Greek, and Roman history, which were adopted by prominent public schools. Keightley aimed to create educational materials that improved upon existing works, and the widespread adoption of his textbooks by institutions like Eton, Harrow, and Rugby suggested his success. He also engaged in literary criticism and editing, producing annotated editions of classical authors like Virgil and Horace, as well as Ovid and Sallust. His critical biography and annotated edition of John Milton's works further cemented his reputation as a serious scholar, with his insights on Milton's mythological allusions continuing to be referenced in later studies.

Keightley's scholarly approach was characterized by a comparative analysis of myths and tales, seeking patterns and connections across cultures. However, he was also pragmatic, considering the possibility of independent development of similar narratives. His contributions to Thomas Crofton Croker's 'Fairy Legends of South Ireland' led to a complex situation regarding credit. While he contributed tales, one notable story, 'The Soul Cages,' was later revealed by Keightley himself to be largely his own invention, adapted from a German tale. He confessed this in a footnote in a later edition of 'Fairy Mythology,' demonstrating a degree of intellectual honesty despite the initial lack of full disclosure. This episode highlights the evolving landscape of authorship and attribution in early folklore studies.