When creating a metallic gradient in Illustrator, you will first need to create a gradient palette. To do this, open the Gradient Editor by clicking on the Gradient tool in the Toolbar and selecting the Gradient palette from the menu that pops up.
Next, create a new gradient using the linear gradient tool and select the first color from the gradient palette. Drag the color up and to the left until you reach the desired gradient point.
Then, hold down the Alt (Option) key and click on the next color in the gradient palette to add it to the gradient. Repeat this process until all the colors in the gradient palette have been used.
Once the gradient is complete, select the gradient and press the Control (Ctrl) key to select the entire gradient. Then, Shift-click on the gradient to add a new anchor point at the top-left corner of the gradient.
Finally, drag the gradient downwards to create the metallic look.
You can also add a metallic sheen to objects by applying a metallic gradient to the object and then applying a sheen effect to the gradient.