Doctor Lesko

 created the Fire Ants that carried off or killed almost everyone in Grayditch. He was experimenting to return giant ants to their normal size through genetical manipulation and accidentally created the fire ants. Despite the death and destruction his experiments caused, Lesko remains indifferent to the lives lost, as he states "at the cost of a few; generations shall be saved", and is far more concerned with the preservation of his experiments than of human lives. Lesko doesn't even express concern for the lone survivor of the ant attacks, Bryan Wilks, the son of the man who built Lesko's shed and moved his equipment into it. Killing Lesko will result in negative karma despite what an uncaring person he is.

Lesko has a shack by the diner which requires Average Lock-picking Skill, or the key to enter. He can be found deep underground in the Marigold Station. He is involved in the quest Those! which can be obtained from him or alternately you will be approached by Bryan Wilks who will trigger this quest, Doctor Lesko's quest offers either Ant Sight or Ant Might as a reward, the player can choose between the two. Lesko can sometimes be killed by fire ants if you leave both doors to his office open, close them after speaking to him to ensure he is not killed before you have completed his quest.

Note: If you don't select the extra payment option during the quest, you cannot obtain Lesko's Lab Coat. Killing him after completing the quest will net just a loss of Karma. The clothing he has on him is just a normal Lab Technician Outfit.

Appearances
 only appears in Fallout 3.

Bugs

 * It has been reported that Lesko has been found dead by some players before you start the quest, so it is suggested that one does not wait too long to complete the "Those!" quest until the exact parameters of this bug has been discovered and hopefully repaired.
 * This bug can be fixed in the PC version by clicking Lesko's corpse in console mode and typing "resurrect".
 * You should get the Ant Might / Ant Sight perk immediately when offered by Doctor Lesko. If you delay getting it until Doctor Lesko is back in his shack, you might not get the dialogue option to get the Ant Might / Ant Sight perk. Also, adding the perks Ant Might (000C1A6B) or Ant Sight (000C1A6C) through the console, the fire resist may not be added to your character.
 * Sometimes Lesko's hair color will switch between blond and brown, although this could be a result of shading.

Trivia
Doctor Weston Lesko is likely named for Matthew Lesko, an author who compiles books on how to take advantage of government programs. Matthew Lesko enjoys something of a local cult celebrity status in the DC area, due to his wacky television commercials and question-mark-covered vehicles and clothing. Matthew Lesko's website is http://www.leskobooks.com/

More likely he is named after "James R. Lesko" a character from the Film Phase IV who is also a scientist who has to deal with "Ant Problems".

Doc Lesko's voice also seems to share an unmistakable similarity to that of resident "Simpsons" 'Mad' Professor, Professor Frink, and to Professor Hubert J. Farmsworth from "Futurama". Doctor Lesko also bears a certain facial and vocal resemblance to Doctor Isaac Kleiner from the Half-Life franchise. This may a homage to any or all of these characters.

After completing Dr. Lesko's quest when he is 'permanently' in his lab shack in Grayditch; his parting thought when speaking to him 'Now was it five parts per milliliter or six ... hmmm' can be considered a nod (and a nerdy version) of the line made famous in Dirty Harry movie 'Now was it five shots or was it six; in all the excitement I've lost count... well, do you feel lucky punk, do ya?'

Related quests

 * Those!
 * Nectar Collecting for Fun and Profit