|Affiliation:||German Federal Intelligence Service|
|Significant other(s):||Collette Stenger (Ex-girlfriend)|
|Played by:||Henry Ian Cusick|
|First episode:||"Day 5: 7:00pm-8:00pm"|
|Last episode:||"Day 5: 8:00pm-9:00pm"|
Before Day 5
Theo was trained by MI6. Six months prior to the events that took place in Day 5, Theo Stoller came to the United States to take part in a covert operation. He built a romantic relationship with information broker Collette Stenger to gather intelligence on her terrorist clients around the world.
During Day 5, Theo Stoller was in his hotel room with Collette Stenger (who was secretly brokering a deal for Russian separatist Vladimir Bierko). They were in bed together but she took a call from Bierko. After the call Theo pulled her close so they could finish making love.
A few minutes later at 8:11pm, Theo asked to learn about Stenger's secret and lucrative work, explaining that he's like to help her with it in some way. Collette became defensive and insisted she didn't talk about her work. He then diverted her attention by announcing news from Maria, their real estate agent, concerning a villa in Positano. Stenger told Theo she would meet him at the Van Nuys Airport before leaving to meet her client.
Theo left and discovered armed men storming the hotel. When the armed men treated Theo as a hostile, Theo threatened to shoot one of them, Curtis Manning, if they didn't stand down.
After it was confirmed that the armed men were agents with CTU Los Angeles, Stoller revealed that he was an operative for German Intelligence. When Jack Bauer told him that Stenger was working with a known terrorist planning to strike America within the next few hours, Theo refused to cooperate. He had been building his case for months and giving up Stenger would blow up the operation.
When Bauer offered to get the WET List for Theo, he agreed to give up Stenger. Stoller's agency had been wanting the list for some time, but the American government refused to give it up. After Chloe O'Brian sent the list to Jack's PDA, Stoller started to cooperate and told Jack where he was meeting with Stenger.
When Bill Buchanan and Karen Hayes demanded for Jack to get the WET list back, Stoller pulled a gun on him. After Jack told Karen that there was no other way to stop the next attack, Stoller believed he wouldn't be double-crossed. When Stenger arrived, Stoller stalled her in order for CTU to identify her. After Stenger was taking into custody, Stoller drove away.
Theo called his German contact, and asked him to inform his superior, Heinrich, that he now had something he has wanted for a long time. While uploading the WET list to his superiors, the memory card self-destructed inside his PDA, destroying it. Jack subsequently called Theo to apologize. He promised to help him rebuild his case once the national security crisis was over, but Theo refused to believe him and angrily hung up.
- Theo: Finish this. ("Day 5: 7:00pm-8:00pm")
- Jack: Theo, it's Jack. I'm sorry.
- Theo: We had a deal.
- Jack: When this is all over I promise you I will help you rebuild your investigation. I give you my word.
- Theo: I had your word. Now I know what it's worth. ("Day 5: 8:00pm-9:00pm")