Dr. Kleiner

Overview
Doctor Isaac Kleiner is a scientist and one of the main characters of Half-Life 2, alongside being a Resistance member. He was one of the few survivors of the original Black Mesa Incident and an experienced hand at teleportation and inter-dimensional travel.

Plot
Dr. Kleiner is first seen in Point Insertion, on a computer monitor after being called by Barney Calhoun. He expresses his amazement at the return of the player, Gordon Freeman, and chats with Barney for a little while, pointing out that Gordon must reach Dr. Kleiner's lab through any means necessary.

He later appears in his lab, searching for his pet headcrab Lamarr, where he, alongside Gordon, Alyx Vance and Barney all meet up, with Kleiner intending to send the player and Alyx straight over to Eli Vance's lab. After a chat, Gordon is introduced to his newly refurbished HEV suit by Barney and Kleiner, and not long after, they meet up in the teleportation room in Kleiner's lab.

Alyx is sent over to Eli's lab fairly easily, but as the player attempts making it over, Lamarr shows up and effectively trashes the teleporter, causing Gordon to repeatedly teleport in various locations, including Dr. Breen's office. After a few teleportations, Gordon appears behind Kleiner, who is naturally startled by his appearance.

Afterwards, he doesn't appear for a while, until Nova Prospekt. Alyx programs the Combine teleporter to Kleiner's lab, where Kleiner can be heard over a radio or other device. After a while, Gordon and Alyx arrive at Kleiner's lab, but they appear to be locked in the teleporter room. Alyx knocks on the blast door, where Kleiner peeks through the door with a shotgun in hand. After nearly blasting Alyx across the room, he expresses his shock that Alyx and Gordon have arrived, apparently being unsure how or when they arrived. He then explains that both Alyx and Gordon were missing for a full week, revealing that apparently Kleiner's teleporter has become very slow.

After a chat, Barney arrives on a computer screen, requesting the assistance of Gordon and Alyx. Alyx mentions that she will meet up with Barney soon, but first she must get Dr. Kleiner to a safe place, to which Kleiner's procrastination stalls them both again. His last appearance is in "Follow Freeman!" at a building overlooking the Overwatch Nexus. Armed with a Laser Rifle, he teams up with Gordon and friends, to take down the Nexus and suppression field. He acts like a standard Rebel, only with less health. Due to this, he generally doesn't survive long enough to even reach the Nexus.

Gameplay
Kleiner only appears as a fighting ally once in the game; during the aformentioned sequence in 'Follow Freeman!' just before the nexus. Kleiner has the same AI as most ordinary Rebels, but unlike said Rebels, he is armed with a Laser Rifle, allowing him to do considerable amounts of burst damage. This is hard to take advantage of, however, due to his low HP; he generally dies after only a handful of shots. Should he survive taking a bullet or two, it's recommended to bring him a medkit as soon as possible, if you wish to take advantage of his rifle.

In addition, he tends to yell random humorous statements while fighting.

Trivia
Dr. Kleiner is the only ally in the game that spawns with a Laser Rifle.

Kleiner seems to enjoy snacks, as a total of six can be found in his lab, three on his desk, three in an item crate (though the latter three can only be found after Nova Prospekt).

While armed, Kleiner often makes humorous responses to various things, such as screaming 'HUAUGH' whenever he spots an enemy, or randomly saying 'Gordon!' while in combat.