10 Times Doctor Who Has Broken Its Own Rules
2. Cold-Blooded Murder
The Doctor doesn't use guns. The Doctor doesn't kill. Ever. Apart from when they do.
The Tenth Doctor is perhaps the most notable of the modern Doctors to abhor violence - and guns in particular. Much of Series Four's arc featured the Doctor referencing 'no guns' and suffering the consequences of those who used them. The Doctor's Daughter and The End of Time both saw the Tenth Doctor on the edge and ready to shoot, but he withdrew from cold-blooded murder.
The Twelfth Doctor... not so much. 2015's Hell Bent featured the Doctor breaking his own rule and pulling a gun on the Time Lord General - someone he had fought alongside during the Time War and was effectively on his side. Prepared to stop him from saving Clara, the General suffered the Doctor's wrath - gunned down in cold blood.
Despite the Time Lord's ability to regenerate, and the Doctor having previously checked which regeneration the General was on, this murder was still brutal and totally uncalled for. With audiences having witnessed the Doctor's arduous and heartbreaking 'deaths' over the years, and aware that everything about the Time Lord changes upon regeneration, this murder was particularly thoughtless.
The Doctor has been known to kill others too, gun or no gun. 2012's Dinosaurs on a Spaceship is notable for the Eleventh Doctor's cruel and explosive defeat of Solomon, and the Thirteenth Doctor spared no time in leaving mutant spiders to die in 2018's Arachnids in the UK. Even the Fugitive Doctor introduced in 2020 didn't shy away from guns.
However, a death caused recently by the Thirteenth Doctor has far more thoughtless and cold ramifications...