The 45 is a nickname given to President Donald Trump by his critics as a way to refer to him and the administration without invoking his actual name. The number 45 signifies the ordinal number of Donald Trump's presidency in counting order since the establishment of the office in 1789.
Origin
The association between the number 45 and Donald Trump was established shortly after his victory in the presidential election in November 2016. One of the earliest notable instances can be attributed to Trump himself, who was seen sporting a custom edition of his iconic Make America Great Again red baseball cap with "45" embroidered on the side while leaving his Florida resort on November 27th, 2016.
However, the widespread usage of "45" as a pejorative nickname for President Trump was first introduced by American actor Laurence Fishburne during his guest appearance on Comedy Central's The Daily Show With Trevor Noah on January 26th, 2017.