Geiger has racked up almost 150 appearances for Hoffenheim’s first team and was once considered a future German international.
“It’s the chance for a restart, a new beginning,” he said. “I want to push myself out of my comfort zone and take on this new challenge.”
Asked what kind of player “passionate” Aberdeen fans will see, Geiger suggested: “I like to be aggressive, but I believe in my technical ability. I’ve got a strong mentality. I want to win in everything I do.”
Pfannenstiel is delighted with the Scottish Premiership club’s sixth signing of the January transfer window.
“Dennis will bring real energy and tenacity to the squad,” he said.
“I’ve known him since his early years at Hoffenheim, so I know what type of character he is.
“He has played at the highest level so brings a real pedigree and attributes, which I believe can help improve us.”
Aberdeen had already added Afeez Aremu from Kaiserslautern and Lyall Cameron, on loan from Rangers, to their midfield options.
Goalkeeper Per Kristian Bratveit has also been brought in from Stromsgodset), while forward Toyosi Olusanya is on loan from Houston Dynamo and defender Liam Morrison from Queens Park Rangers.
