Zeus is one of the three skins released under the Heavens of Olympus part of the Olympus offer. It could be purchased as part of an item deal for a limited time in early September 2017.
Zeus could be purchased for $19.99 in the "Best Deal!" which included the Hades skin and either 50000 coins (Browser) or 1800 DNA (Mobile). It was not available for individual purchase and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.
Note: The Heavens of Olympus sub-offer was released again for a limited time in early October 2019. The price for the “Best Deal!” was lowered to $14.99 on browser and remained at $19.99 on mobile. The original included game currency on either platform was replaced with a package of 1200 DNA.