Bowler hat

A bowler hat was type of hat.

A Time Lord messenger dressed as an English businessman, complete with bowler hat and umbrella, appeared to the Third Doctor to warn him that was on Earth. (TV: Terror of the Autons)

The Fourth Doctor wore a bowler hat whilst investigating Fang Rock lighthouse. (TV: Horror of Fang Rock)

Whilst visiting Victorian England to look into "the Crimson Horror", the Eleventh Doctor wore a bowler hat. (TV: The Crimson Horror)

On Earth, the Council of Dead wore identical pin-stripe suits and bowler hats to cover their horns. (WC: Snowfall, Attack of the Snowmen)