Sega announced today that it has acquired San Francisco-based independent developer Three Rings Design, best known for the success of its MMO release Spiral Knights.

The publisher noted that the acquisition is set to play a key role in its "aggressive expansion" into the digital space, as Three Rings joins Sega's other subsidiaries Football Manager developer Sports Interactive and Total War creator The Creative Assembly.

Sega said that it plans to continue support for Spiral Knights, and also aid Three Rings in launching its upcoming Doctor Who: Worlds In Time MMO alongside BBC Worldwide.

Three Rings was originally founded in 2001, and has worked on a number of PC titles over the past 10 years, including Puzzle Pirates and social world Whirled.

Haruki Satomi, SVP at Sega of America, said "We knew from the first time we saw Spiral Knights that the team at Three Rings was not simply talented but truly unique, and the close bond we have formed with them over the past year has only solidified that impression."

"We are proud to welcome them as the newest member of the Sega family, (Spiral Knights Gold)and look forward to seeing what great things we can create together over the coming years."

Three Rings' Daniel James added, "We are honored to be joining such a legendary team and look forward to collaborating on amazing ideas together."