From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
Wallace Gray is one of President Roslin's senior advisors, and the man credited with regulating the internal economy within the Fleet, making sure vital food and medical supplies were fairly distributed throughout the fleet (Colonial Day). Gray may also be responsible for drafting the means to re-introduce currency-based commerce within the fleet (Kobol's Last Gleaming, Part I).
Despite this work, he is still seen by some as either a "prince of darkness" wielding the power behind Roslin, or as a "fatuous gasbag" (Colonial Day).
When Tom Zarek is nominated as a candidate for the position of Vice President, Roslin persuades Gray to stand against him (Colonial Day). While Wallace has a set of policies - his Mission Statement - which is strong enough to win Roslin some support, Gray's style of presentation and approach to the role of candidate for Vice President is hardly dynamic, and he is unable to secure the nomination against Zarek as Roslin had hoped.
As a result of this, and after hearing a radio interview by Dr. Gaius Baltar, Roslin asks Gray to step down as a candidate, to be replaced by Baltar.
While he does withdraw his candidacy, Gray is far from happy about doing so, and his long-term friendship with Roslin suffers severely as a result. He has not been seen in any capacity since.