Van Toffler, the programming executive who has had a hand in guiding MTV and other Viacom-owned cable outlets since the late 1980s, said he would step down from his post as president of the division that includes MTV VH1, CMT and Logo in April to start a new venture as an independent producer. His departure comes as Viacom is wrestling with ratings shortfalls at a number of its flagship networks.

Toffler (pictured, above, right, with Viacom CEO Philippe Dauman) is expected to stay with the company until sometime in April, and will remain as an executive producer of several flagship events, including MTV’s annual Video Music Awards and the annual CMT Awards.

In an internal memo to staff, Toffler said he expected to start a new company known as Below The Radar, which he said would be devoted to “platform agnostic content creation and acquisition.” Viacom had asked the executive to renew his contract, according to a person familiar with the situation, but Toffler felt the time was right to focus specifically on content given the dizzying number of new distribution venues that have risen through the advent of new technology.

Viacom is expected to detail later this week how its music group will shift following Toffler’s depature, Dauman said in a memo.

“His infectious good nature, insatiable curiosity, creativity, and playful and charismatic leadership style have made Van an admired and respected colleague and a mentor to all who worked with him and for him,” Dauman said. “I will continue to count him as a good friend and close advisor.”

His departure is announced as Viacom is grappling with several issues. During the company’s last call with investors,  Dauman suggested the company would be reducing headcount at its operations as it seeks to realign its staff with the demands of a rapidly changing media industry that has become more dependent on revenue from digital media and subscriptions rather than the advertising that has typically fueled its coffers. Viacom has also indicated it is working quickly to devise new products and content methodologies that are less reliant on traditional measures like Nielsen audience ratings. The company’s networks, including MTV, have seen shortfalls in those metrics.

The spine of another holding, Comedy Central — the latenight combination of Jon Stewart’s “Daily Show” and Stephen Colbert’s “Colbert Report” — is being stretched. Colbert left the network late late year to prepare for his role as the successor to David Letterman on CBS’ “Late Show,” while Stewart announced last week that he intended to leave his program sometime between July and the end of 2015. Comedy recently launched the well-received “Nightly Report” in Colbert’s 11:30 p.m. timeslot and has indicated “The Daily Show” will continue with a new host at its helm.

Toffler has spent years at MTV, where he is known for his oversight of many of the network’s landmark series, including “Unplugged,” the music-concert program that invited artists to play in acoustic and unvarnished fashion. He was also instrumental in the launch of MTV Films, a unit that has produced such properties as “Election,” “Hustle and Flow” and “Napoleon Dynamite.”

During his tenure, Viacom’s music-related networks have launched everything from “The Osbournes” to “Party Down South.”

Toffler has held a succession of positions at MTV. He was appointed president of Viacom’s Music and Logo Group in 2004. Prior to that, he served as president of MTV & MTV2. In 1999, Toffler oversaw the relaunch of MTV2 and helped guide the acquisition of CTN: College Television Network in 2002, relaunched as mtvU, an MTV-themed network for college students. He also supervised properties including VH1 Classic and Palladia.

[Updated, 9:38 AM PT]