Which Power Rangers series debuted in 2011?

The Power Rangers series that debuted in 2011 was Power Rangers Samurai.

Power Rangers Samurai premiered on Nickelodeon on February 7, 2011, making it the franchise's seventeenth television entry. It was the first Power Rangers season produced by Saban Brands after Haim Saban reacquired the franchise from The Walt Disney Company.

The story follows five Samurai Rangers defending Earth from the Nighloks, monsters connected to the Sanzu River. Jayden of the Shiba Clan leads the team as the Red Ranger, joined by Kevin, Mia, Mike, and Emily. The season adapts footage, costumes, and concepts from the Japanese Super Sentai series Samurai Sentai Shinkenger.

Power Rangers Super Samurai is the follow-up season, not the original 2011 debut. Ninja Storm premiered in 2003, and Megaforce followed in 2013. Samurai also marked the franchise's move to Nickelodeon and was the first season shot and broadcast in widescreen HD.