Dropped by Drowned occasionally (exclusive to Bedrock Edition).
Gold ingots can be used to craft Armor, Weapons and Tools. Gold armor is typically impractical. While it offers slightly more protection than leather armor, it has very low Durability. Similarly, a gold sword deals the same damage as a wooden sword, but has a lower durability.
Gold tools can break a block faster than any other tool material, but it is not necessary to craft as gold tools are very fragile. They can perform any task their wooden tool equivalent can, but gold is much harder to come by than wood, which makes them somewhat impractical.
Gold tools, swords and armor tend to receive better Enchantments than their counterparts.
Before Beta 1.2, gold tools had both low speed and durability. Currently, gold tools have a higher speed than Diamond and can break blocks about twice as fast as wood tools.
Because it's a rare drop by zombie pigmen, gold ingots are considered a renewable resource.
In Minecraft: Pocket Edition, gold ingots were previously required to make the Nether Reactor Core structure. It required 36 golden ingots (all crafted into blocks). However, this feature has now been removed from the game.