Dr. Wu is a character from Army of Two: The 40th Day. He appears in the 4th chapter, The Hospital. He is a doctor working at the last functioning hospital in Shanghai.
Rios and Salem meet him after Salem knocks himself unconscius and Rios takes him to the hospital, where Dr. Wu apparently saves Salem. While he is still unconscious, Dr. Wu tells Rios what he knows about Jonah. When Salem wakes up 24 hours later, Dr. Wu tells the duo that he dislikes mercenaries, but he needs their help. Since he helped them he wants them to turn the hospitals back up generator on and then hold off the soldiers trying to get in while he himself evacuates everyone. Rios agrees to help him if Wu helps them get out of town afterwards.
Depending on if the player made positive choices in the three Morality Choices Dr.Wu will mention that he heard good things about Rios and Salem and he'll open a locker that contains a G18c, debatably the best sidearm in the game. However if the player made negative choices he will not give Rios and Salem any weapons.
Telling Rios and Salem to save any hospital staff they see, he will keep an eye on them through the headset. When Rios and Salem finally return (with or without Chin) he will tell them to hold off the soldiers in the lobby and after that he thanks them for their help and tells the duo to head for the mall. If they can't get out of town from there, he can't help them.
Near the end of the game if you saved enough civilians they will return to help you. Rios and Salem notes that they are from the hospital and they will have to thank Dr. Wu if they make it.
- Dr.Wu's name may be a play on "Dr.Who" a popular British TV series