(written from a Production point of view)
Mark Rosenthal was credited as co-writer of Star Trek VI: The Undiscovered Country, along with Leonard Nimoy and Lawrence Konner. He and Konner have been writing partners since 1985. Nimoy later alleges, in his book I Am Spock, that Konner and Rosenthal actually had nothing to do with the finished script, but the studio gave them credit for political reasons.
Rosenthal made his writing debut alongside established television writer Konner with the motion picture The Legend of Billie Jean (featuring Dean Stockwell). This was followed by such films as The Jewel of the Nile, Superman IV: The Quest for Peace, The Beverly Hillbillies (starring Diedrich Bader), and Mercury Rising (featuring Kevin Conway).
More recently, Rosenthal and Konner worked on the remakes for Mighty Joe Young (featuring Lawrence Pressman and Scarlett Pomers) and Planet of the Apes (featuring Erick Avari, Cary-Hiroyuki Tagawa, and David Warner). Their latest films were Mona Lisa Smile and Flicka.