The Koenig brothers are identical triplets who are all agents of S.H.I.E.L.D., clearance level 6. In the aftermath of the Battle of New York, they received assignments from Director Nick Fury to become guardian agents for Fury’s secret bases, and are thus three of the very few people whom are privy to Fury being alive, and whom still accept direct orders from him and his successor, S.H.I.E.L.D. Director Phil Coulson, for whom they share a mutual fanboy excitement over. It has been mentioned that they largely pass the time prior to The Uprising by playing the Call of Duty video game with each other.
Agent Eric Koenig was the first brother to be introduced, in 1×18 Providence. He is the guardian agent for the base codenamed "Providence", located somewhere in the Canadian wilderness. After The Uprising, he received instructions from Nick Fury to expect Agent Phil Coulson at Providence, and was alarmed when Coulson brought along five other fugitive S.H.I.E.L.D. agents, with a sixth appearing soon after, none of whom had been personally vetted by Fury. After putting all the tagalongs through a lie detector "orientation", Eric, while handing out new S.H.I.E.L.D. identification in the form of security lanyards, started tracking the whereabouts of his new colleagues. He was unfortunately murdered by Hydra sleeper agent Grant Ward less than a day later, with the "Providence" base itself compromised and revealed to the U.S. government by former S.H.I.E.L.D. Deputy Director Maria Hill
Agent Billy Koenig appeared in 1×22 Beginning of the End, after Coulson’s promotion to Director of S.H.I.E.L.D. gave him access to Fury’s cube, in which the coordinates of a second secret base, codenamed "The Playground", was revealed to be under Billy’s care. It is here that Fury sent Agents Leo Fitz and Jemma Simmons to ahead of the rest of Coulson’s team before heading off to deal with his former protegee, Hydra sleeper agent John Garrett. It can be assumed that Billy will fulfill the role of administrative agent while Director Coulson commands "The Playground" as the new S.H.I.E.L.D. HQ.
Agent Sam Koenig has so far (as of July 31, 2014) first appeared in the introductory video first available at the Marvel TV SDCC panel 2014.  He appears alongside surviving triplet brother Billy Koenig, as they discuss the return of S.H.I.E.L.D. Agent Bobbi Morse
His first appearance in the show is in Ye Who Enter Here (2×09) where he coordinated with Billy to secure Raina and extract her to the Bus.