What was the last name of the person who was a founder of the Group of Seven?  Answer the above question based on the context below:  In October, MacDonald introduced Thomson to Dr. James MacCallum. A frequent visitor to the Ontario Society of Artists' (OSA) exhibitions, MacCallum was admitted to the Arts and Letters Club in January 1912. There, he met artists such as John William Beatty, Arthur Heming, MacDonald and Harris. MacCallum eventually persuaded Thomson to leave Rous and Mann and start a painting career. In October 1913, MacCallum introduced Thomson to A. Y. Jackson, later a founder of the Group of Seven. MacCallum recognized Thomson's and Jackson's talents and offered to cover their expenses for one year if they committed themselves to painting full time. MacCallum and Jackson both encouraged Thomson to "take up painting seriously, [but] he showed no enthusiasm. The chances of earning a livelihood by it did not appear to him promising. He was sensitive and independent, and feared he might become an object of patronage." MacCallum wrote that when he first saw Thomson's sketches, he recognized their "truthfulness, their feeling and their sympathy with the grim fascinating northland ... they made me feel that the North had gripped Thomson as it had gripped me since I was eleven when I first sailed and paddled through its silent places." He described Thomson's paintings as "dark, muddy in colour, tight and not wanting in technical defects". After Thomson's death, MacCallum helped preserve and advocate for his work.Thomson accepted MacCallum's offer under the same terms offered to Jackson. He travelled around Ontario with his colleagues, especially to the wilderness of Ontario, which was to become a major source of inspiration. Regarding Algonquin Park, he wrote in a letter to MacCallum: "The best I can do does not do the place much justice in the way of beauty." He ventured to rural areas near Toronto and tried to capture the surrounding nature. He may have worked as a fire ranger on the Mattagami reserve. Addison and Little suggest that he guided fishing tours, although Hill finds this unlikely since Thomson had only spent a few...
The answer to this question is:
Jackson