Theodore "Teddy" Srisai (born in 1995) is Lauren's younger and only brother and brother-in-law of Stu. He is the son of Fong Srisai, who constantly praises him for being a child prodigy and presumably the only doctor in the family.
Teddy is a 16 year-old premed student at Stanford University. He is considered a child prodigy by his father, Fong Srisai. He entered Stanford because his father had him done the entrance exams early. He works out at Bally Total Fitness in Palo Alto, California.
Lauren asks Stu to take Teddy with them on their "safe" pre-wedding brunch for a beer and marshmallows, and he becomes the misplaced one (like Doug) at the party in this outing as a result of the group blackout. It turned out he was trapped in the Bangkok hotel elevator, as a result of the blackouts the city usually suffers when he went to the 17th floor to get some ice for his cut finger. He was rescued by the trio and suffered from extreme heat and found the keys for Chow's speedboat. While riding on Chow's speedboat, he accepted that, when he woke up, he was kind of happy. Teddy then found the missing pictures from the night before on his iPhone, as his phone was dead for two days and he recharged it and found all the photos, even of him cutting his own finger.
- Teddy did not return in the third film, making the second film, his only appearance in The Hangover franchise.
- In real life, the actor that portrays Teddy is actually Chinese not Thai, and he is the son of director Lee Ang.
- Cut off finger while drunk
- Suffered extreme heat while locked in an elevator