Guccifer 2.0 turns out to be GRU 2.0.
Guccifer 2.0, doxer of the Democratic National Committee during the 2016 US elections, is confirmed to be what he (actually they) was long suspected to be, a team of GRU operators, Russian military intelligence (Ars Technica). It was difficult to track Guccifer 2.0 because of their use of Elite VPN, an anonymizing service headquartered in Russia exiting through a server in France. At least once, however, Guccifer 2.0 forgot to activate the VPN client before logging in, revealing an IP address traced to a GRU facility on Moscow's Grizodubovoy Street.
Guccifer 2.0 posed as a disinterested Romanian hacktivist, but few took this claim at face value. Among those who did, more or less, were some political advisors to the Trump campaign. Special Counsel Mueller has brought FBI agents who worked on Guccifer 2.0 onto his team (Daily Beast).
Motherboard, which long ago offered strong evidence suggesting Guccifer 2.0 wasn't what he claimed to be, says the missteps that betrayed their identity were unsurprising: "Guccifer 2.0 was always sloppy" (Motherboard).