HBO has given a production commitment to the limited series “I Know This Much Is True” starring Mark Ruffalo.

The six-episode series is based on Wally Lamb’s New York Times bestseller of the same name. It is described as a family saga that follows the parallel lives of identical twin brothers in an epic story of betrayal, sacrifice, and forgiveness, set against the backdrop of 20th century America. Ruffalo stars as twin brothers Dominick and Thomas Birdsey.

Ruffalo will also executive produce in addition to starring. Derek Cianfrance serves as writer and executive producer as well as director, with Lamb also executive producing. Ben Browning and Glen Basner of FilmNation Entertainment, Gregg Fienberg, and Anya Epstein will also executive produce. Lynette Howell Taylor and Jamie Patricof will co-executive produce.

Ruffalo was most recently seen in the blockbuster film “Avengers: Infinity War” in the role of Bruce Banner/The Hulk. He is a three time Oscar nominee, Tony Award nominee, and Emmy Award winner. His film credits include “You Can Count on Me,” “Eternal Sunshine of the Spotless Mind,” “Collateral,” “Spotlight,” “The Kids Are All Right,” Infinitely Polar Bear,” “Now You See Me,” and “Foxcatcher.” His television credits include HBO’s “The Normal Heart” for which he won the Emmy for best television movie as an executive producer. His theatre credits include “This is our Youth,” “Awake and Sing” and Arthur Miller’s “The Price.”

He is repped by UTA, Lighthouse Management, and KlevanLongarzo LLP.

Cianfrance’s previous credits include “The Place Beyond the Pines” and “Blue Valentine,” both of which starred Ryan Gosling. He is repped by CAA.

Lamb is the author of six New York Times best-selling novels, including “I’ll Take You There,” “We Are Water,” and “Wishin’ and Hopin’.” Lamb also edited “Couldn’t Keep It to Myself” and “I’ll Fly Away,” two volumes of essays from students in his writing workshop at York Correctional Institution, a women’s prison in Connecticut, where he has been a volunteer facilitator for the past 18 years.