Dr. Leo Spaceman (/spəˈtʃɛmɨn/, US dict: spə·chĕm′·ɪn—except by Tracy, who pronounces his name like the English word "spaceman") (Chris Parnell) is a graduate of the Ho Chi Minh City School of Medicine. He practices questionable medicine, such as giving a "medical professional's seal of approval" to a defective "meat machine"; despite his obvious shortcomings, Jack is unwavering in his support of Spaceman's "skills". He wrote a bestselling book, The Cigarette Diet, and found shocking medical abnormalities during Desert Storm which his boss refused to report to Saddam Hussein. At one time Spaceman dated Lynette "Squeaky" Fromme, whom he described as "difficult".
Lenny Wosniak (Steve Buscemi) is a private investigator occasionally hired by Jack. He first appears in the second-season episode "The Collection", where (while spying on Jack to determine if he has any skeletons in his closet which could prevent him from being named the new CEO of General Electric) he discovers Jack has a large collection of homemade cookie jars. Jack also hires him in the third season to obtain personal information about a man his mother was seeing, and (later) the true identity of his father.
Donald (Michael Benjamin Washington) is an entrepreneur who pretends to be Tracy Jordan's son (despite being two years older than Tracy). His money-making ideas consist of questionable business practices, such as picking out corporate names already in use (a frozen-yogurt and microbrewery restaurant called Microsoft, and a phone service for nationwide air-quality updates called American Airlines). Tracy knows Donald is not his son; he supports his misguided ideas anyway, and Jack (who had convinced Tracy to cut Donald off) later tells Tracy to keep being a dad.
The following is a supplementary list of recurring characters—including those appearing briefly in multiple episodes, such as a regularly-appearing writer—about whom little is known.
* Lee (Tom Broecker) - The show's costume manager; appears in eleven episodes. He is also a costume manager on 30 Rock.
* Stage manager (Teddy Coluca) - Appears in six episodes
* Rachel Baze (Rachel Hamilton) - One of the writers on the show; in "The Aftermath", Jack mentions her last name and that she just became engaged. She has speaking parts in two episodes.
* Anthony (Anthony Atamanuik) - One of the writers on the show
* Donald (Donald Glover) - A stagehand on the show; has a speaking part in two episodes.
* Matt (Matt Dickinson) - Jack's assistant in two season-one episodes and one season-three episode (in place of Jonathan)
* Stage manager (Brendan Walsh) - Shouts "Shut it down!" at the end of each of the two episodes he appears in (referred to in credits as "Shut It Down").
* Alfonso/TGS Piano Player (Jeff Richmond) - Jenna's pianist. He appears in "Ludachristmas" and "Christmas Special". Richmond also appeared in "The Aftermath" and "St. Valentine's Day." He also appears as the TGS piano player in the first-season episode "The Baby Show". Richmond is the primary composer on 30 Rock and Tina Fey's real-life husband.
* Tim Grandy - One of the writers on the show; in "The Aftermath", Jack mentions he is from Bowie, Maryland. He has a brief speaking part in "The C Word".
* Grace Park (Charlene Yi) - An NBC page who has a slight romantic history with Kenneth. Appeared in "The C Word".
* Moonvest (Craig Castaldo) - A homeless man. He appears in "The Head and the Hair", "Audition Day", and "I Do Do". His name is a reference to Leslie Moonves (president of NBC's competitor CBS Corporation) and avant-garde street musician Moondog.