According to legend, Martin of Tour was a soldier in the army of Constantine the Great serving in Gaul, near the French city of Amiens, in the fourth century. On a winter's day Martin encountered a poor beggar at the city gates and cut his military cloak in half to help shield the shivering man from the cold. The night after his act of charity, Martin had a vision that Christ came to him wearing the part of the cloak he had given to the beggar, saying: "What thou hast done for that poor man, thou hast done for me." Martin, who had converted to Christianity as a child but who had entered military service at his father's behest, then left the military to devote his life to the Christian faith.
This oil sketch, which depicts the moment of Martin divided his cloak, was long believed to be executed by Anthony van Dyck around 1620 to 1621. The artist treated the subject in large scale twice over the course of his career—once for the parish church of Saint Martin in Zaventem and once for his friend Peter Paul Rubens. However, examination of the panel and the panel maker's mark indicate that the panel would not have been available for the painting prior to the late 1630s. The sketch also cannot be attributed to a later stage of Van Dyck's career, owing to certain dissimilarities with the master's work, such as the scratching technique used to indicate the decorative pattern on Saint Martin's armor—a method Van Dyck never used.
However, the Gallery's panel does exhibit certain similarities to an oil sketch by the Antwerp painter Jan Boeckhorst. Boeckhorst, who was enormously influenced by Van Dyck's style and may have known his compositions of the subject. The subject of the painting would seem also to have appealed to Boeckhorst, whose family had extremely close ties to the Church of Saint Martin in his native city of Münster. It is possible he painted this sketch in anticipation of a commission for that church that was never realized.