Thomas Gallagher (?-1898) was an early member of City Council.
He was also the City Clerk and Treasurer in 1855 and 1856.
There was also a Thomas Gallagher who was the postmaster when the post office's name was changed from Contra Costa to Oakland in 1855. This Thomas Gallagher also opened a dry goods store on Broadway this same year. 1
Note also that a Thomas Gallagher had a saloon on Broadway early in the 1850s.1
It is likely, but by no means certain, that these are all the same person .
1. Past and Present of Alameda County California, Chapter XX, Oakland