Jeff Colby (born Jeffrey Broderick Colby) is the most decent member of the Colby family. In Denver, he works for his manipulative uncle Cecil and gets closer to Fallon, his crush from his childhood. He has no idea his marriage is nothing more than a business deal between the Carringtons and the Colbys and, therefore, he puts up with his wife's wimps and affairs. Their frequent disagreements tear their marriage asunder, and it seems increasingly, so he starts considering himself just a dupe who's easily taken advantage of.

Knowing that the Colby name is soiled enough through the foggy kindness of his uncle's pathetic schemes, Jeff decides to incline towards "Denver-Carrington" and to leave "ColbyCo. Oil" behind. Furthermore, he's willing to divorce Fallon and to get custody of his unborn son Little Blake mostly as a consequence of Fallon's sexual and emotional maladjustment.

After a very short and hasty affair with troubled Claudia Blaisdel, caused by her need of lost hopes regarding Lindsay, Jeff seeks source of comfort in Kirby. As a nice girl who's dreaming about the real man and real love, Kirby draws his attention to herself quite fast and they get married in spite of the fact that she's carrying Adam 's child. Not anticipating Adam's evil side of personality, Jeff is deceived once again, contaminated with a neurotoxin and emotionally hurt, especially after he has realized a mockery of his marriage, but the true sorrow and lack of purpose will be the result of Fallon's awful getaway on the very day of their wedding. Prior to that, Fallon had a fatal affair with the playboy Peter De Vilbis. Revelation that she run off the wedding and died in a plane crash with Peter, devastated Jeff, leading him to turn to bottle and sleep around.

Trying to forget her, although ineffectually, Jeff becomes interested in one adventuress Nicole Simpson yet their relationship ends as fast as it has started - overall, having no prosperity. He was also involved with Lady Ashley until she was killed in Moldavia, but all the time he was haunted with the fact that Fallon is alive.

And then, all of a sudden, Fallon's and Colby's paths seem to intersect - preparing to receive 50% of "Colby Enterprises" shares from his aunt Constance, Jeff finds Fallon in Los Angeles and he'll fight for her learning that she has lost her memory and married his half brother Miles. In addition to that, he'll also find out from his mother Francesca that his father is Jason Colby and not his brother Philip. In the beginning he holds a grudge for the Colby family, but in time he accepts Jason as his father and becomes closer to them, particularly closer to Miles after a great deal of conflicts and outbursts of jealousy.

Married but not so happy, Jeff and Fallon return to Denver where Fallon's UFO experience is going to lead their relationship to another rupture, and, as for Jeff himself, he decides to participate in "Vitron Oil" project much more actively which means cooperating with Leslie even sexually, then to help Blake in disclosing the "Nazi Treasure" plot and to marry Sammy Jo eventually. Sammy Jo is, however, only his new exit to relief and despite their love, Fallon is the one who's been chosen by Jeff's heart since their childhood. After he's been released from "The Consortium", they decide to stay together - this time for good. Being a young man, successful in business, respected by the Carringtons and the Colbys, Jeff has been working for both "Denver-Carrington" and "ColbyCo. Oil". His relationship with Fallon will grow more serious and more stable over the years. They share two children, Little Blake and Lauren.