Dr. Gero is another evil scientist from the Dragonball Z series; however, it is not the same one that was killed by his own androids more than 1,000 years earlier. It could be a distant descendant of his, wanting to fulfill his ancestor's legacy.
Much like Professor Utonium, his colleague, his early years are shrouded in mystery. However, it is obvious from his name he was a scientist and a doctorate in college.
He sided against the government during this event, which turned out to be a fatal error for him and Utonium. As the Saiyans drew closer, they developed Proto-Metal Sonic in the hopes of subduing the Saiyans. Corey fought this, and won after unlocking his hidden powers. Knowing that Corey would likely kill them if the explosion didn't, they left holograms of themselves, escaping in pods similar to that of Dr. Eggman's design. He was on the run for five years, the stress taking its toll on him.
Courtesy of a convenient flashback in Episode 12, we learn that Dr. Gero was Android #16. He stated he'd much rather fight the Saiyans himself, knowing he would die either way. He is killed when the cousins and the Eds combine their signature moves, obliterated completely along with #15.
His final day was spent making the cousins Corey and Drew feel pain, and even absorbing some of their energy. It is unclear of what his true final thoughts were before he got swallowed up by the beam and killed.