R. Martin Klein, also credited as Robert Martin Klein, Robert Klein, Bob Klein, and in earlier dubbing work under the alias Bob Marx, is an American voice actor whose career in the industry began around 1981. His professional background extends beyond voiceover to include work in theater and film productions. Known for his flexible vocal range, he has been based in Los Angeles for much of his time in the dubbing industry, which began in earnest around 1995.

Klein is perhaps best recognized for his extensive and long-running work within the Digimon franchise. He provided the voice for the Digimon Gomamon and its evolutions, including Ikkakumon and Zudomon, a role he has portrayed across multiple series and films. His work in this franchise began with the original Digimon: Digital Monsters and Digimon Adventure 02 and continued through Digimon Data Squad, Digimon Fusion, the Digimon Adventure tri. film series, and the theatrical release Digimon Adventure: Last Evolution Kizuna. He also voiced additional characters within the Digimon universe, such as Toshiaki Mori in Digimon Tamers, Professor Haruhiko Takenouchi in Digimon Adventure 02, and various other creature voices across the series. Another notable role from this period is Katsuhiko Jinnai, the flamboyant antagonist from the El Hazard series.

In addition to his franchise work, Klein has voiced characters in numerous other significant anime productions. He played the stalker Me-Mania in the acclaimed psychological thriller film Perfect Blue. As the user noted, he performed the role of Fukurou in the science fiction series Noein - to your other self. His other major anime roles include Flint Hammerhead in Flint the Time Detective, Ivan Whisky/Cyborg 001 in Cyborg 009, Marumaro in Blue Dragon, Gaku in FLCL, and Jidan Nickard in Mobile Suit Gundam: The 08th MS Team. He also appeared as Impy in Mon Colle Knights, Kotaro Nanbara in Hand Maid May, Kakipi in Magical Meow Meow Taruto, and Grisor in Zatch Bell!.

Klein has also contributed to the English dubs of several video games. His work in this medium includes roles such as Harald Hoerwick and Marlo in the.hack series, Hideyoshi Toyotomi in the Warriors Orochi series, Lias Warren in Star Ocean: First Departure, Mugetsu in The Bouncer, and Ganz Rothschild in Radiata Stories. He also provided voices for characters in Dynasty Warriors 4 and Samurai Warriors.

Beyond Japanese anime and video game localization, his voice work can be found in western animated projects as well. He voiced Iggy D'Iguana in the series Animalia and was the voice of Edison the Firefly in several LeapFrog educational DVDs. He also performed voice roles in the Lego Star Wars special The Padawan Menace. A notable achievement in his career is his voice direction and performance work on the English dub of the Gatchaman franchise, as well as his sustained, decades-long association with the Digimon series as the voice of Gomamon.