In the original series pilot, Dr. Smith was not a bumbling coward. He was portrayed as intelligent, evil and manipulating.
from Fandom:
Filmed in black-and-white, the first season of Lost in Space took itself more seriously than subsequent seasons—at least at the outset. Set in 1997, the series begn}}s the Robinsons, a family of space travelers preparing for a five-year exploratory voyage to the Alpha Centauri star system in the Jupiter 2. Unfortunately, the enemy saboteur Dr. Zachary Smith (Jonathan Harris) intends to prevent the mission and kill the family, with the help of the Robot, which he programs to carry out his plans to destroy the ship.
When the Jupiter 2 blasts off, Dr. Smith is trapped inside the vehicle with his intended victims: Prof. John Robinson (Guy Williams); his wife, Maureen (June Lockhart); his children, Judy (Marta Kristen), Will (Bill Mumy), and Penny (Angela Cartwright), and ship's pilot Don West (Mark Goddard). Because of Smith's sabotage, the ship veers off course to an unchartered planet where the Robinsons et. al. will spend the remainder of the season.
Contrary to fan belief, it had never been intended to kill off the Dr. Smith character after the first five-episode story arc (Jonathan Harris confirmed, in a 1997 interview with STARLOG magazine, "I was hired to be in every episode.") The Robot "reforms" and becomes an unending fount of valuable information for the space castaways, periodically bursting forth with cries of "Warning! Warning!" and "Danger! Danger!" and dealing with matters beyond his ken by muttering metallically, "That does not compute."
As for Smith, he evolves from snarling villain to cowardly buffoon, whom the others inexplicably tolerate, even though Smith's perfidy and duplicity cause nothing but trouble for them. The notion to serialize the episodes is dropped early on in favor of self-contained stories, though each episode ends with a cliff-hanger preview of the following week's installment. Unlike the next two seasons of Lost in Space, guest stars were kept to a minimum during season one.
