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, acting 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 reaction leading to her downfall. (DW: The Christmas Invasion)