Nicholas Courtney, who played Doctor Who’s longest-running character – Brigadier Alastair Lethbridge-Stewart – has passed away at age 81 after battling cancer.

Courtney is best known for his beloved Doctor Who character Brigadier Alastair Lethbridge-Stewart, a companion of the Doctor who helps defend Earth from alien threats and serves as commander of the United Nations Intelligence Taskforce (UNIT).

A veteran of the Doctor Who, Courtney starred opposite of five different Doctors appearing in 107 episodes over an interrupted period of 24 years.

Former Doctor Tom Baker described Courtney as a “wonderful companion.”

“Of all the characters in Doctor Who there is no doubt that he was the most loved by the fans,” said Baker.

Courtney even appeared in the Who spin-off series The Sarah Jane Adventures in 2008, reprising his colourful character The Brigadier. His dedication to the programme earned him a position as honorary president of the Doctor Who Appreciation Society in 1997.

Not just limited to a single role, Courtney has appeared and starred in a number of shows including The Avengers, Callan, The Champions, and Minder.

Remembered by many in the business as a “true gentlemen,” Courtney is survived by his second wife Karen and children Philip and Bella.