WWF took full advantage of their situation, unifying the World Championship (formerly the WCW World Heavyweight Championship) and WWF Championship at WWF Vengeance 2001, with Chris Jericho becoming the first undisputed champion in over 50 years. The championship was then represented by the belts of its two predecessors until a singular belt design was commissioned. By May 2002 the WWF had been renamed to World Wrestling Entertainment and the WWE Undisputed Championship, as it was now called, became the top championship of the promotion. The title would go on to be held by Triple H, Hulk Hogan, The Undertaker, The Rock, and finally Brock Lesnar.
With the purchase of WCW during the previous year, WWE's roster had doubled in size and with newly obtained properties and a desire to further expand, the promotion was essentially divided in what became known as the WWE Brand Extension. This resulted in WWE's two main programs, Raw and SmackDown, becoming distinct franchises or "brands", acting as complementing promotions under WWE. The WWE Undisputed Championship was then consequently shared between both brands and soon conflict began brewing over the title. In late August 2002 after becoming the youngest WWE world champion at the time by winning the WWE Undisputed Championship, Brock Lesnar and his title were secluded to SmackDown. Meanwhile, the Raw brand was left without a top championship of their own. To remedy this, a new world championship was established for the brand and named the World Heavyweight Championship. With now a new prominent world championship on the Raw brand to complement the SmackDown brand's world championship, the WWE Undisputed Championship had become disputed, which resulted in the title simply becoming known as the WWE Championship.
Holding 2 top titles(Heavyweight and WWF) meant that his undisputed. After WWF was called WWE(for legal reasons) the title was unified into Undisputed. When Brock left to Smackdown, Raw was left with no major title, and Smackdown had Undisputed championship. Because of that, another major belt was created(Heavyweight) for Raw. Because of that another major title Undisputed championship became Disputed, so they just changed Undisputed Championship with WWE championship. So we have now two titles.