(written from a Production point of view)
Joseph L. Scanlan directed four episodes of Star Trek: The Next Generation. After directing four episodes and seeing how out of control the cast would act when not filming, Scanlan walked out and refused to ever direct any further episodes of TNG again and he never did. 
Scanlan has also directed episodes of Spenser: For Hire, which starred Avery Brooks (Benjamin Sisko from DS9), and Quantum Leap, starring Scott Bakula (Jonathan Archer from ENT). He also directed an episode of Gene Roddenberry's Earth: Final Conflict.