Orlin was an ascended Ancient who showed the people of Velona how to construct advanced weapons to defend themselves against the Goa'uld. After the Goa'uld threat had been averted the people began to plan the conquest of other worlds. The Others of Orlin's kind came and wiped them out to "correct" Orlin's mistake—sentencing him to live alone on the desolated planet.
While hiding out in Samantha Carter's house Orlin builds a small, single destination Stargate and returns to Velona. Where the others have returned, he tells Sam, and have given him a second chance. They help him to Ascend once again to an ethereal form, and he destroys the weapon and leaves. (SG1: "Ascension")
Orlin constructed a small, one-use Stargate using 100 pounds of pure titantium, 200 feet of fiber optic cable, seven 100,000 watt industrial-strength capacitors, items from Sam's house, and more. He encoded it to only dial Velona, and expected that it would probably burn out after it was used. He was also able to create a perfectly cut rectangular emerald out of some of Carter's household items and her microwave oven.
Whether or not the gate still works, it will no doubt be invaluable to Earth -- showing them how to construct a Stargate from material found on Earth, and without Naquadah. It is likely that Colonel Simmons had the gate confiscated from Carter's basement and brought to Area 51.Even when he became an ascended being again, he continued to check in on Carter from time to time. He decided to descend when Earth was in grave trouble, exposed to the Ori plague. This time, an adolescent boy was the only form he could take, to be able at the same time to retain the knowledge he aquired while Ascended. He started to help them building a cure. (SG1: "The Fourth Horseman, Part 1")