|First Appearance||"Just an Old Fashioned Lab Song" (1998)|
|Voiced by||Paul Williams|
- "Through mathematics and science skill, Dexter, you've mastered the arpeggio!"
- — Professor Williams
Professor Williams is a character appearing in the second season episode "Just an Old Fashioned Lab Song." He is a piano teacher hired by Mom and Dad to provide him with music lessons. Both his singing and speaking voice is provided by singer-songwriter Paul Williams, to whom the character bears several physical similarities, most notably his diminutive stature, which is roughly parallel to the height of Dexter.
Much to Dexter's annoyance, Mom and Dad saddle with him unwanted piano lessons. Upon his arrival, Professor Williams mimics Dexter's every move before entering, and nonchalantly uses Dee Dee as a clothes rack. For his first lesson, he tries to teach Dexter how to play an arpeggio. Professor Williams is unperturbed by Dexter's reluctance to play. Upon the conclusion of their lesson, Williams asks Dexter to practice arpeggios until their next lesson. Dexter practices relentlessly as seasons of the year pass; eventually, he succumbs to nightmarish delusions about Professor Williams attempting to do him harm.
Mistaken for Dexter by a laboratory security measure on account of his physical similarities to him, Williams finds himself in Dexter's laboratory, and is amazed by what he sees. Though Dexter tries to make him leave, Williams points out to him that his inventions emit sounds reminiscent of music; in a flash of inspiration, Williams performs the song "Breathe in the Sunshine," about a glorious union of music and science. Williams leaves, assured that Dexter has learned to appreciate music. He is immediately proven wrong as Dexter quickly discards his new attitude and breaks the musical machinery with a giant wrench.