Nathaniel Colgan MRIA, a self-taught botanist, was known for his research on the ‘real’ shamrock and for his encyclopaedic survey, The flora of the county Dublin. Little was known of his early life and family or of his interests beyond botany, marine biology, mountaineering, and his day-job. He was remembered for being shy, but perhaps it was more a case of being reserved on account of his personal background. When he was 14, he and his siblings were orphaned and brought up in the Coombe, Dublin. Held in high esteem by his peers, he rose to become a Member of the Royal Irish Academy. This study uncovers his hidden past, from the grandfather whose silk-weaving business waned to his espousal of Gaelic culture: a founder of the Feis Cheoil movement and a member of the Gaelic League, he was the subject of a secret police report when he supported the promotion of a member of the Volunteers as his successor as head clerk in the Dublin police court.