The preternaturally youthful Wulff, 51, who once described himself as no "alpha male" has governed the state of Lower Saxony, home to automaker Volkswagen, since 2003.
Merkel's choice for president, he won election by a special body in a vote seen as a test of her authority after a dire start to her second period in office marred by internal squabbling and a crisis in the eurozone.
Allies of Merkel feared Wulff could use Lower Saxony, a high-profile perch, as a possible launch pad to pose a challenge to the weakened chancellor. But she has now effectively neutralised him, at least for the four-year length of his term, by placing him in a golden cage far removed from the real instruments of political power.
However, Wulff required three rounds of voting to secure the appointment as members of Merkel's ruling coalition rebelled against his candidacy and delivered her a damaging political setback.
The German president, ensconced in Berlin's Bellevue Palace, serves as a kind of moral arbiter for the nation, receiving state guests and occasionally weighing in with contemplative speeches on the issues of the day.
Though popular with a significant national profile, the so-called "Kennedy from the Leine" after the river flowing through his state's capital Hannover, was never before called to serve in Berlin.
Observers say the genial Wulff does not have the killer instincts of a true political animal and is well-suited for the presidency.
"I lack the absolute will to power and the willingness to subordinate everything else," he famously said in a magazine interview in 2008 when asked whether his ambitions included laying down the gauntlet for Merkel.
Merkel, a fellow Christian Democrat (CDU), was thought to breathe a sigh of relief, as the blond trained lawyer with elegant dress style and a gentle sense of humour has demonstrated his appeal to voters.
He became active in the CDU at the age of 20, and was just 34 when he first challenged Gerhard Schröder, who would later become chancellor, for the premiership of Lower Saxony.
It took him two tries but he eventually wrested control of the state in 2003 from Sigmar Gabriel, Schröder's crown prince and current leader of the Social Democrats.
He left his long-time wife Christiane in 2006 for public relations executive Bettina, who is 15 years his junior, and launched a charm offensive to mollify his conservative base after the shock announcement. Bettina's tattoo on her upper arm has raised eyebrows in some corners of the German press.
They are now married and have a two-year-old son, in addition to a teenage daughter from Wulff's previous marriage.
Merkel said she would be delighted to imagine the sound of children's laughter ringing through the Bellevue Palace. She has now got her wish.