"Oh Jay-zus-'n-Mary!"
Liam O'Connor is the team's Field Operative. He was supposed to die on the Titanic in 1912. He was saved by Foster. He is the member of the team who travel in time to observe and then prevent time contamination. He works with the two support units: Bob and Becks. He has a close relationship with Bob because Liam is the Operative and therefore has to be in prolonged company of Bob. This leads to the two having a close friendship, even as far as Bob being able to alter his mission priorities to save Liam.
"Death"
Liam was aboard the Titanic when it was beginning to sink. he was down on the E deck searching for survivors. he realised he had waited too long and was doomed. He was panicking as he had always hated water when Foster appeared and saved him.
Foster
It is revealed in Day of the Predator that Liam is actually Foster. In effect, he saved himself on the Titanic.
TimeRiders
In the very first book Liam is rescued from the Titanic by Foster. He is taken to headquarters, and is introduced to his role as Mission Operative. He goes back in Time with Foster and Bob to delay Kennedy's assassination, as a training routine. Then their training is cut short by a time wave. He travels back to the 1940's where Kramer has led Germany to victory in WW2. He is taken prisoner and taken to a concentration camp. Seperated from Bob, he misses all return windows. Liam is then rescued by Bob, who has many followers who think he is an angel of the Lord. Eventually Liam and Bob leave a message for Maddy and Sal in the Museum near all the visitors books, telling them where to open a time window. They successfully get back, right in the middle of an attack from the "human" race. He helps get rid of them for long enough to open up another time window and are sent back again to where Kramer entered. Bob stops Kramer, but is damaged beyond repair. Liam is forced to cut out Bob's silicon computer chip, a gruesome job for Liam. He comes back and helps clean up the bunker. Sal said in her notebook that "he looks older and grown up than before his mission."
The Truth
The Truth is that this is SPOILER ALERT!!!