Maruo Arima, also known as "Maru", is the user of the Beast Gaia Memory to become the Beast Dopant and an antagonist in episodes 31 and 32 of Kamen Rider W. He is also Suzuko Arima's husband.
He was portrayed by Katsuya.
Kamen Rider W
He is a bank robber who a decade ago, attempted an armored car robbery at the Futo Dam with his wife Suzuko. The case was investigated by Soukichi Narumi until the evidence went dry and when Isamu Bito turned himself in for the crime. By the present, now rich, Maruo is still looking for a bear statue that holds the Zone Memory. However, he meets resistance from Kamen Riders Double and Accel, but he defeats them easily. Once the Zone Memory returns to Suzuko's possession, the two return to the Futo Dam to finish their heist, after quickly besting the Riders. There, they face Accel once again, but just when it seems Maruo and Suzuko are going to win, Double arrives. Double pushes himself to his limit fighting Maruo, and beyond, achieving Double's perfect synchronization form; CycloneJoker Xtreme. The Beast Dopant is weakened by Kamen Rider Double CycloneJoker Xtreme's Prism Break Maximum Drive before being eventually defeated by the Bicker Charge Break Maximum Drive.
OOO, Den-O, All Riders: Let's Go Kamen Riders
In the altered timeline where Shocker achieved global dominion, the Beast Dopant is one of the monsters that served the organization in the alternate 2011.
Super Hero Taisen Z
The Beast Dopant was among the revived monsters serving the Space Shocker.