Oliver is Anna Harcourt's ex-boyfriend.
In "Phoenix" after Anna's murder Nikita found a photo of Oliver and Anna on the internet. She learned that he works as a bartender in a bar in Washington. She went to see him. He told her that she broke up with him 5 months ago, cause she was hiding something from him. After the break up he followed her to an elite club which way way out of her price range.
Nikita later returned to give his Anna's dog, Yoshi.