J. Robert Spencer is an American actor and singer primarily known for his extensive work in musical theatre, though he has also performed voice roles for anime productions. Born Robert John Spencer on February 12, 1969, he is a Tony Award-nominated actor who gained prominence on Broadway.

His most recognized voice acting role is Seita in the English dub of the acclaimed Studio Ghibli film Grave of the Fireflies. In this 1988 animated war drama, Spencer provides the voice for the teenage protagonist who struggles to survive with his younger sister in Japan during World War II. The English-language version featuring Spencer was distributed by Central Park Media. Beyond this iconic role, his other anime voice credits include providing voices for Mabo and a Messenger in Amon Saga, as well as voicing Masao Sera in The Vanilla Series.

While his anime voice work is limited, Spencer's primary career has been in live performance. He graduated cum laude from the Shenandoah University musical theatre program in 1991 and later received an Honorary Doctorate of Fine Arts from the institution in 2009. His Broadway debut came in 1997 as a swing in the musical Side Show. He originated the role of Nick Massi in the original Broadway cast of Jersey Boys in 2005. Perhaps his most celebrated stage role was as Dan Goodman in the Broadway musical Next to Normal, for which he received a Tony Award nomination for Best Actor in a Musical. He also received a Helen Hayes Award nomination for his performance in the same role at Arena Stage. In 2014, he starred as Abraham Lincoln in the New York Musical Theatre Festival production of Bayonets of Angst and won an award for Outstanding Individual Performance. His television appearances include roles on Law & Order, Law & Order: Special Victims Unit, and All My Children.