Alastair Lethbridge-Stewart

A parallel Earth's version of the Brigadier, Brigade Leader Lethbridge-Stewart was a high ranking member of the Republican Security Forces, and in charge of security at the Eastchester Scientific Labour Camp.

Biography
Unlike his counterpart, the Brigade Leader had a missing or damaged left eye, covered by an eyepatch. He captured and interrogated the Third Doctor, who had just arrived from his own universe. At first he had trouble believing the Doctor's story of having come from another dimension.

It eventually became clear that the Doctor had been telling the truth and the penetration of his Earth's crust would devastate the planet beyond recovery. He threatened to shoot the Doctor unless he rescued himself, Section Leader Shaw and Petra Williams, but instead Shaw shot him dead with her own pistol to save the other Earth. (DW: Inferno)

He is mentioned in the episode The Wedding of River Song. While on the TARDIS, the Doctor calls the hospice where Brigadier Lethbridge-Stewart spent his last years. Unfortunately, he had passed away a few months before the time when the Doctor called. He reportedly died peacefully, spoke frequently about the Doctor, and always had his nurses pour him an extra glass of brandy in case the Doctor came by.

Behind the scenes

 * Nicholas Courtney, of course, played the part without the Brigadier's trademark (false) moustache.
 * Dialogue in Inferno only refers to the Brigade Leader by his title and last name, but not by his first name. Presumably, he had the same first and middle names as his counterpart, but this remains unclear.