You do not truly know someone until you fight them.—Seraph, The Matrix Reloaded
It is known that when Seraph came to The Matrix he began to work for The Merovingian. When he was working for The Merovingian The Oracle approached him and asked him to protect her. Ever since, The Merovingian has seen him as a traitor.
A program that appears as a human of Asian descent, Seraph behaves as a guardian, similar to a computer login screen, to protect access to more important programming; it challenges anyone for the proper credentials. In this case, Seraph fights the challenger, allowing those with sufficient fighting skill (and the rightful reasons to access) to meet The Oracle.
Neo is summoned by The Oracle and arrives at a teahouse, where Seraph waited. Seraph apologizes to Neo in advance before launching a furious attack to test Neo's true skill, and as such his authenticity.
Seraph is apparently unable to ward away an event that cost The Oracle her "shell" or avatar that most of the Zion operatives were familiar with (not realizing that The Oracle is actually a program and not a bluepill). The event left The Oracle with a different appearance and Seraph apparently needed for other purposes. The Exile accompanies Morpheus and Trinity in tracking down The Trainman and The Merovingian in a successful quest to free Neo from Mobil Station.
Despite a successful fight against Agent Smith in another time and place, Seraph (who attempts to guard Sati as well) is no match for the now-rogue agent, who assimilates him as he does everyone--program or human--that he encounters, including The Oracle herself.
After Neo's successful quest to the Machine City to barter a peace, The Matrix is reloaded, and Seraph, Sati and The Oracle are restored to the proper personas and appearance.