Who ran against Donald Trump in the 2016 and 2020 US presidential elections?

Former US President Donald Trump is in the race for the White House and is securing his second term against his Democratic rival Kamala Harris. Trump, who served as the 45th President of the United States, is contesting his third consecutive election campaign.
In 2016, Trump defeated Hillary Clinton, while in 2020 he lost to Joe Biden.
2016 presidential election
Former First Lady and Secretary of State Hillary Clinton lost to Donald Trump despite winning the popular vote by more than 2.8 million votes. Trump won 304 electoral votes to Clinton's 227, after an aggressive campaign that violated political norms.
During his campaign, Trump blamed the party establishment for costly interventions in foreign conflicts, the growing gap between rich and poor, stagnant real wages, excessive political correctness and the lack of enforcement of immigration laws.
Meanwhile, Clinton's campaign featured excellent organization and fundraising—and nearly every poll on election night pointed to a comfortable victory for her. However, Trump's anti-Washington appeal to white, working-class voters outside major cities in key industrialized states proved to be a key factor in what several publications called “the biggest upset in American history.”
2020 presidential election
Incumbent President Trump lost to Joe Biden in the 2020 presidential election, which took place amid the global Covid pandemic.
Biden received more than 81 million votes, won the popular vote by more than seven million ballots and triumphed in the Electoral College by 306 votes to 232.
Trump refused to accept the election results, claimed without evidence that the election was stolen from him through fraud, and launched unsuccessful legal challenges in several states he lost.
Widespread acceptance of Trump's continued baseless claims that the election was stolen ultimately led to the storming of the U.S. Capitol by Trump supporters on January 6.