He is a Piper, and the character must be that of a simple but engaging Scot. Although his smile disarms opposition, he is on occasions a man of action who will defend his friends or principles fearlessly. He is cheerful, open, manly, flexible - more flexible in fact than Ben and Polly. When either Ben or Polly are pulling his leg, he reacts with 3 grin. Because of his romantic appearance, he always wears the Kilt - his hair is longer and his shirt has a swashbuckling appearance: because of this and the attractive features of his character he must assume the part of the Young Hero in each story.
He must be constantly amazed and perplexed that he is wandering through Space and Time and is coming up against things, even common-place things, which he could never have dreamt of in his day. The large things - planes, computers, etc., rock him back on his heels - he finds it hard to comprehend them at all.
He brings many of the attributes of the Highlander of his period with him, being courageous, impetuous, superstitious and romantic. His impetuosity often provokes difficult situations for the time-travelers, but his direct approach will sometimes help solve problems as well as create them.
His superstitious background enables him to relate the forces of evil being fought by the Doctor to the witches, demons, goblins, etc., of his native land. Sometimes, in fact, this folklore gives him a deeper insight into the forces opposed to the travelers than the more scientific approach of the Doctor, Ben and Polly.
BBC Character Outline. 28 November 1966.