Gold
Gold (GC aka Gold Coins/Galactic Credits) is of vast importance to your empire. Every [Unit|unit] and [Building|building] requires gold to build. It can also be used to invest into your empire's research, in addition to or in place of Research Centers.
Smaller quantities of gold are also required to send out Exploration Ships and military fleets. Because of the significant role Gold plays in the galactic economy, many empires dedicate themselves entirely to Banking. Bankers focus primarily on the production of as much gold as possible, either for their own benefit or as a critical part of a [Family|family]'s economic strategy.
Gold can be produced by building Cash Factories, and/or by taxing Population.
Any gold you have on hand each tick is partially destroyed by Bureaucracy. This 0.5% per tick expense is intended to encourage a more active playing style, with more wars and less saving up for weeks on end. Bureaucracy can however be partially avoided by storing low bids on The Galactic Market that people are not likely to sell to. Unlike other Resources, gold will not decay while on the market like this. However, there is a still a 10% withdrawal fee for taking bids off the market so this strategy may or may not be effective depending on the circumstances.