Ian provides the series with an action-orientated figure, able to perform the physical tasks that the elderly Doctor cannot. The Doctor rarely calls him by his first name (Ian) as the others do but rather as his surname, Chesterton. There was also a small number of instances where William Hartnell, mistakingly calls him Chesterfield. His concern, above all, is for the safety of the TARDIS crew, and in the early stories he often takes issue with the Doctor's habit of placing the group in harm's way just to satisfy his own curiosity. The chemistry between Barbara and himself is also evident, although the nature of their relationship is never made explicit in the television series, and their eventual marriage is only revealed forty-five years later.