Alex Klein

Alex Klein 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. (DW: The Christmas Invasion)