The fourth Doctor is a lively, bohemian adventurer with a great passion for his travels in time and space. His clothes are decidedly eccentric: a light grey wool coat trimmed with black felt on the collar and cuffs, matching baggy grey trousers tucked into brown calf-length boots, a cream and brown waistcoat, open-necked shirt and a long scarf that has to be looped round his neck many times to keep it out of the way of his feet. The ensemble is topped off by a wide-brimmed black felt hat. He has a wild-looking face, blue eyes and a mass of unruly curly brown hair.

Odd-looking as he is, the Doctor is a hugely charismatic figure, able to make friends easily with a winning smile and a touch of humour. He will inveigle himself into hectic situations before the participants even have time to realize there is a stranger among them, offering help or advice and sometimes even tinkering before anyone can stop him. Witty comments, puns and offerings of jelly babies are the Doctor's weapons against a hostile greeting.

His genius, however, is erratic: the Doctor is temperamental and prepared to be bluntly rude to anyone who interferes with his work. He tends to be absent-minded, leaving behind or sometimes losing vital pieces of equipment. And his companions often take the blame for his mistakes. Like his previous incarnation, he dislikes those in authority.

The Doctor is constantly bubbling with ideas and responds quickly to the stimulus of new information. He asks questions of other people at random, often with no apparent connection, in his attempts to buy time while he thinks through a problem. He adopts this approach even in adversity: any captor is likely to be subjected to a stream of seemingly inane observations or witticisms while the Doctor plans his escape.

This incarnation of the Doctor is more of a loner than previous ones: he regards companions as a hazard because they require too much safeguarding. Yet their tendency to wander into danger is sometimes the Doctor's fault: he has a habit of withholding important information while he tries to work out what is going on.