Jack "Action Jack" Barker was a main character in seasons 3 & 4 in HBO's Silicon Valley.
Jack is first mentioned by Monica in the episode Founder Friendly as being the new replacement CEO of Pied Piper after Richard was voted out of by the board members of Raviga. He then appears later in the same episode when Erlich Bachman goes to meet him at the Raviga offices in an attempt to intimidate him with jokes based towards his age.
Richard then goes to visit Jack at his home to inform him that Richard intends to turn down the position of CTO at Pied Piper. Due to this Jack no longer has an interest in being the CEO because of Richards work on the algorithm, however Richard then reconsiders his position and agrees to stay as CTO leading Jack to accept the position of CEO.