Sylvia Tilly from Star Trek: Discovery arguably owes her origins to Reginald Barclay from Star Trek: The Next Generation. Star Trek: Discovery introduced Tilly, played by Mary Wiseman, as Michael Burnham's talkative, self-conscious roommate in season 1. Since her introduction, Tilly has carved out her own unique places in the hearts of Discovery fans. Throughout the show's three seasons, Tilly has demonstrated her brilliant mind and bubbly personality, become one of Michael's closest friends, and even risen to the rank of Discovery's acting first officer in season 3.
Unlike Tilly, the character of Reginald Barclay was not a main character on Star Trek: The Next Generation but is remembered as one of the show's quintessential guest characters. Played by Dwight Schultz, Barclay was introduced in the season 3 episode "Hollow Pursuits" and went on to have a role in four subsequent Next Generation episodes as well as six episodes of Star Trek: Voyager and a brief cameo in Star Trek: First Contact. His introverted personality and nervous behavior belied a competent officer, and under the guidance of both Captain Picard and Lieutenant Geordi La Forge, the audience witnessed Barclay begin to come out of his shell and demonstrate his capability.
Barclay and Tilly both share many similar personality traits, but the comparison between the two runs deeper. Barclay was developed because Star Trek creator Gene Roddenberry felt that Star Trek: The Next Generation was in need of a "relatable" character, someone who was "just like the rest of the human race" in Dwight Schultz's words. Roddenberry felt that the niche for such a character had not yet been filled on TNG. Characters like Captain Jean-Luc Picard or Counselor Deanna Troi were people that the audience could aspire to be like but weren't "relatable" in the sense that any viewer could see a fair amount of themselves in them. Barclay, by contrast, was written to have a number of human failings. He had hypochondriac tendencies, lacked self-confidence, and had a hard time relating to his coworkers. All of these traits are things that anyone can struggle with, so Barclay provided fans with someone they could both identify with and look up to.
As Gene Roddenberry predicted, people responded well to Barclay. However, since the end of The Next Generation, no other character in the franchise has been imbued with the same level of relatability until Tilly. There were a few minor characters on subsequent Star Trek shows that exhibited some similar traits, but they tended to be contained to one episode here and there. Tilly, however, is a fascinating evolution of Barclay's legacy. The two are not exactly the same, but Tilly displays many of the same attributes that drew fans to Barclay. She is highly intelligent, but also unsure of herself, eager to please, and slightly lacking in social graces. All of these characteristics combine to make her not only relatable but charming and enjoyable to watch. Luckily, because Tilly is one of the main characters on Discovery, the show has allowed her personality to shine and given her storylines priority, something that Barclay never got to the same extent.
Star Trek: Discovery's decision to have a "relatable" character be a part of the main cast instead of just a recurring guest demonstrates that the show is aware of how well the idea of a more down-to-earth character plays with fans. Before Star Trek: The Next Generation's Barclay, Star Trek characters were mostly portrayed as aspirational, not relatable. Now, the road is paved for characters like Tilly to remind the audience that their seemingly more ordinary traits could end up being the source of their strength.