Short answers, pulled from the story.
United Russia was officially formed on the 1st of December 2001 through a merger of the Unity movement and the Fatherland - All Russia bloc. The All Russia movement led by Mintimer Shaimiev joined them as well. The party took its current name at the Fourth Congress in December 2003.
United Russia holds 325 seats in the State Duma, which represents 72.22 percent of the 450-seat chamber. The party has held a majority in the Duma since 2007 and secured constitutional majorities in 2007, 2016, and 2021.
United Russia officially proclaimed Russian conservatism as its ideology at its 11th Party Congress on the 21st of November 2009. In 2015, the party shifted its stated ideology to liberal conservatism. Political scientists describe the party variously as centrist, centre-right, a big-tent party, and a party of power.
Vladimir Putin has never formally joined United Russia as a member. On the 15th of April 2008, he accepted a nomination to become the party's leader while explicitly stating that this did not make him a member. Despite this, political scientists describe him as the party's de facto leader.
United Russia's peak vote share was 64.20 percent in the 2007 State Duma elections held on the 2nd of December 2007, giving it 315 seats. Vladimir Putin headed the party's federal list in that election, though he refused to formally join the party.
The Unity bloc was created in 1999 by Kremlin insiders who wanted to counter the Fatherland - All Russia coalition. Tatyana Yumasheva, Yeltsin's daughter, wrote on her LiveJournal blog that Boris Berezovsky was a founder of the organisation. Sergei Shoigu, then Minister of Emergency Situations, was appointed as the party leader.