Nothing of Wendell Marsh's past is known. He is an agent of H.A.M.M.E.R. and, given his nervousness, presumably a rookie.
Agent Marsh was created by Marjorie Liu and Giuseppe Camuncoli and first appeared in Dark Wolverine #82.
Agent Marsh hasn't appeared since.
Major Story Arcs
As Norman Osborn was preparing for his forces to invade Asgard, Agent Marsh was among the H.A.M.M.E.R. agents who would go into battle against the Asgardian Gods. Terrified of the prospect of going to war, let alone against Gods, Marsh fell ill. Getting the attention of the Dark Avengers' Daken (when he accidentally vomitted on Daken's shoe), Daken reassured Marsh that everything would be alright and he shouldn't worry about anything. As Marsh calmed down, Daken then beat him brutally and Marsh was sent home unable to fight.