[2] Described in the show as tall, lanky and long-haired, Kelso was considered a simple-minded person until he moved to Chicago in the eighth season.

[6][7][8] In spite of his purported stupidity, Kelso is shown on several occasions not to be immature, but merely unmotivated, displaying startling intelligence unbecoming of his usual personality.

Near the end of the series, Kelso becomes one of the first characters to completely break away from adolescence and into adulthood when, as part of the plot-line, he impregnates a girl with whom he had a one-night stand.

To his friends' surprise, Kelso took responsibility for the child, moving to Chicago to take a job to support and be near his new-born daughter.

[9][10] Kelso was first introduced in "That 70s Pilot" as Eric Forman's less intelligent, loudly obnoxious friend who is dating a preppy, younger student, Jackie Burkhart, whom he first met in 1968 playing "Fort."

As the series progresses, it is later revealed that Kelso cheats on his girlfriend (most notably with Pam Macy and Eric's sister Laurie).

[6][14] In later episodes, Kelso is given a neglected 1964 Dodge Van by his uncle, which becomes the main focus of his secondary story during seasons 2 and 3.

[19] The fourth-season premiere episode sees Eric, in a dream sequence, envisioning a possible future with Donna, a woman he has not actually met.

[25] During the Season 4 finale, Jackie misleadingly believes that Kelso is proposing to her, causing him to decide to run off to California.

In Season 6, Kelso is the focus of a major plot twist in which he accidentally impregnates a girl named Brooke in a bathroom at a Molly Hatchet concert.

[39] When Hyde follows her there to propose, he finds Kelso naked, wrapped in a towel, making a comment implying that he and Jackie were about to have sex.

However, when Randy and Fez decide to throw a bachelor party for Hyde after his marriage to a stripper, Kelso is fired due to misuse of police equipment and unprofessional behavior.

They both decide they have a lot of maturing to do, many things to take care of in their own lives and, even though they both admit to loving each other, agree that it is not the right time to get married.

[47] In the sequel series That '90s Show, set in 1995, Kelso and Jackie are shown to be back together and have a teenage son named Jay and are about to marry for the third time.

[48] Among Kelso's most famous personality traits are conceit and sheer stupidity, performing a great number of idiocies on a regular daily basis.

Despite his stupid nature, he shows moments of shining intellect, demonstrating the ability to do fast mathematical division and fixing Red's Pong machine.

During a flashback scene, it is implied that Kelso used to be a bookish, motivated student until Hyde introduced him and Eric to marijuana when they were in junior high.

Throughout the series, Kelso has made a large quantity of moronic quotes and performed many dimwitted blunders, and possesses numerous infantile qualities such as enjoying Christmas specials deemed childish by his peers and fussing when something is preventing him from viewing them.

Like the other teenage male central characters of the series, Kelso also possesses an abundance of "horny" personality traits and appears especially fond of the idea of having sexual relations and the willingness to spoil his virginity results in the impregnation of a librarian named Brooke and the birth of a little girl named Betsy toward the end of the series.

Kelso also likes bands such as Led Zeppelin, Foghat, Deep Purple, Aerosmith, KISS, Ted Nugent, Pink Floyd, AC/DC, The Rolling Stones, The Who and Molly Hatchet.

Kelso's family is frequently referred to by other characters as being a large one, despite only one of his siblings, Casey, actually appearing on-screen throughout the show's run.

John Kelso's office job as a "Senior Executive Statistical Analysis Technician" is unclear and confusing to Michael, who decides to make it up and say his dad is a farmer.