Night at the Museum
They are Cecil Fredericks's two colleagues. Their plan was to get rich before they retired as night guards and to steal the magic tablet, while trying to blame it on the new night guard, Larry Daley. However with the help of the museum's figures, Larry was able capture all three of them. After they were sent to jail, Larry had them work as janitors for punishment.
Night at the Museum: Secret of the Tomb
In the third movie, Gus is noticably older, and is handicapped in a wheel-chair. When Larry comes up to a reformed Cecil asking him about the tablet's history, Gus implies to have reformed but still makes a little hard feelings clear with Larry. Reginald appears to still have hard feelings against Larry too but admits he has too reformed himself.