Alex Klein

Alex was the senior aide to Harriet Jones in Downing Street in 2006. He was with her when she was teleported aboard the Sycorax ship. He acted as a translator until the TARDIS resumed its translation.

Her premiership crumbled when the Tenth Doctor whispered to Alex, "Don't you think she looks tired?" — six words that began a chain of events leading to her downfall. (TV: The Christmas Invasion)