Who is Colonel Hector McCandless from Sharpe's Tiger and what is their importance?

Colonel Hector McCandless learns about Tippoo's massive black-powder mine during a meeting with General Appah Rao and is later captured by Tippoo's cavalry. McCandless keeps his secret until Sharpe arrives and manages to pass the news to him. However, the British command never receives the warning to avoid the city's west wall, where the mine is planted. While in the dungeon and hearing Hakeswill's constant jabbering about things being in scripture, McCandless orders the sergeant to hold his tongue.