The correct spelling of the phrase "third doctor" is /θɜrd ˈdɒktər/. The initial sound, /θ/, is the voiceless dental fricative, which is made by placing the tip of the tongue between the upper and lower teeth and forcing air through it. The vowel sound in "third" is the open-mid unrounded vowel, /ɜ/, which is pronounced with the tongue lowered and tensed in the middle of the mouth. The word "doctor" is spelled with the /d/ sound, a voiced dental stop made by briefly blocking the airflow with the tongue tip against the alveolar ridge.
The Third Doctor refers to a fictional character from the long-running British science fiction television series, Doctor Who. This term is most commonly used to describe the third incarnation of the Doctor, a time-traveling alien who takes on the appearance of a human and explores the universe in a spacecraft called the TARDIS (Time and Relative Dimension in Space).
The Third Doctor is portrayed by actor Jon Pertwee and first appeared on the show in 1970. This particular incarnation of the Doctor is known for his flamboyant and dapper attire, typically consisting of a velvet jacket with bow tie, a frilly shirt, and a cape.
In terms of character traits, the Third Doctor is portrayed as being more action-oriented than his predecessors, often using martial arts skills to defend himself. Due to his prolonged exile on Earth, this incarnation spends a significant part of his tenure working as a scientific advisor to the fictional UNIT (United Nations Intelligence Taskforce) organization, aiding humanity in defending against various extraterrestrial threats.
The Third Doctor's era on the show is notable for its focus on stories set on Earth, resulting in a series of adventures that often involve contemporary settings and recurring characters. This era is also known for introducing the Doctor's iconic yellow roadster, Bessie, as well as for showcasing the Doctor's strong bond with his companion, Sarah Jane Smith.