Short answers, pulled from the story.
Doctor Who first aired on BBC Television Service at 17:16:20 GMT on the 23rd of November 1963, eighty seconds later than scheduled due to announcements about the assassination of US President John F. Kennedy the previous day. The BBC believed many viewers missed the first episode as a result and repeated it on the 30th of November 1963, just before episode two.
Doctor Who was created by Sydney Newman, C. E. Webber, and Donald Wilson. Newman, as head of drama, was mainly responsible for developing the programme. Writer Anthony Coburn, story editor David Whitaker, and initial producer Verity Lambert also made significant contributions to the series.
When a Time Lord suffers mortal injury or is weakened by old age, their cells regenerate into a new body. Memories are retained but personality changes. The serial The Deadly Assassin in 1976 established that a Time Lord can regenerate only twelve times, for a total of thirteen incarnations; the 2013 episode "The Time of the Doctor" depicted the Doctor receiving a new cycle of regenerations to move past that limit.
The original Doctor Who theme was composed by Ron Grainer and realised by Delia Derbyshire of the BBC Radiophonic Workshop, with assistance from Dick Mills. It was released as a single on Decca F 11837 in 1964. Derbyshire built each note individually from cut and spliced analogue tape but did not receive an on-screen credit until the 50th-anniversary episode in 2013.
95 of the 253 episodes produced during the programme's first six years are not held in the BBC's archives, following large-scale destruction and wiping of older material between 1967 and 1978. Audio recordings of all lost episodes survive from home viewers, and some episodes have been recovered from archives in foreign countries and from private individuals.
Jodie Whittaker was the first woman to play the Doctor, taking over the role as the Thirteenth Doctor at the end of the 2017 Christmas special. She appeared in three series, the last of which was shortened due to the COVID-19 pandemic, and made her final appearance as the character in "The Power of the Doctor" on the 23rd of October 2022.