Ian Locke was a member of the Locke Family who lived in Keyhouse with his family. Ian was very sick and had seizures at increasing rate due to a tumor in his brain. When the seizures became as frequent as twice per day, in 1912, his father decided it would be better for him that he'd find peace.
With that in mind, he rents a balloon and has his uncle construct a new key. The three use the balloon to see the world before they use the key to enter the moon where they meet former members of the Locke family. Chamberlin leaves Ian and Harland behind here, in a sort of afterlife.
After Ian's departure, Chamberlin would use the Timeshift Key to see him in the past.