|Not to be confused with Old Man Hobo.|
Dr. Isaac Kleiner is a Caucasian American old man scientist from Half-Life 2 and its episodes. He appeared in a few videos of SuperMarioGlitchy4 released in the year 2014.
Dr. Kleiner is a rather tall old man, he has a gray hair and is partially bald. He wears a white shirt marked with the green word "dsb", dark jeans, black shoes and also black glasses. In the video "Ssenmodnar 6.64 (100k special QNA Edition)", his glasses have blue lenses, and in the episode "SwagQuest", he wears a brown hat after Luigi tells him he looks ridiculous (see below).
This is Dr. Kleiner's first appearance in SMG4's bloopers, in this video he appears in the last skit of the video (#15) as a nerd who is revealed to have been watching the video up until this point, and says it really sucks, not knowing SMG4 is right behind him. Eventually, SMG4 gets pissed, and tosses the nerd out the window.
In this blooper, Kleiner makes a cameo appearance in Mario's mind, in which he's near a flying carpet, while Mario is on this last one and screams "What is happening?!".
In this other episode, Kleiner appears as a news reporter on "Humans News" on a large television to whom Sonic is watching after this last one found it, in Human City. Kleiner reports that an alien (Dr. Dr. Dr. Eggman) has landed in Human City.Mario's party because he doesn't have enough swag, he seeks lessons from Bowser on how to obtain swag. After a few minutes in the lesson, Bowser tells Luigi to change his clothes, to add swag. After four clothes changes, Luigi and Bowser settle on a gangster costume. Then, Dr. Kleiner runs up to Luigi and slashes his clothes off with his crowbar, causing Bowser to force Luigi to fight Kleiner, stating that he "ruined Luigi's swag". Luigi is afraid at first, but gains the courage to the old man, telllling him "You look ridiculous". Kleiner then gets angry and Luigi starts rapping. The old man reminds him that this is a fight, and a short battle ensues. The old man strikes Luigi with a Smashball, who counterattacks with a "Big Gay Dance." Kleiner man then throws a fireball at Luigi, who ducks as it ricochets off a tree, blasting the old man into the air and causing him to crash into a boat, which sinks as Luigi does a short victory dance.
He is run over by Mario.
When Dr. Kleiner is referred as "Old Man", he mustn't be confused with the Old Man Hobo from the video games Pokémon FireRed and Pokémon LeafGreen for the Game Boy Advance, and also with the Old Man who appeared in the blooper "SM64: Cooking with Bowser & Mario 2!" in the part "How to cook: Raisins?".