The Life-Model Decoys or LMD's is a staple of the S.H.I.E.L.D. defensive arsenal. LMD's are non-biological automatons designed to mimic the behavior, appearance and speech of S.H.I.E.L.D. personnel.
A bunch of Life-Model Decoys made up the S.H.I.E.L.D. drop team that accompanied Captain America when it comes to assisting the Avengers and Spider-Man into fighting an Ultron-controlled Super-Adaptoid. Unfortunately for Captain America, Ultron hacked into the communications and told the drop team to deploy prematurely. Ultron takes the opportunity to convert the Life-Model Decoys to serve him causing the Avengers and Spider-Man to destroy them. Ultron later used a Life Model Decoy to serve as a diversion by having it pose as Ultron so that Ultron can hack into J.A.R.V.I.S. and Avengers Tower.
The Life-Model Decoy that Ultron corrupted has taken his Ultron nano-virus corruption to other parts of the world.