Who is currently serving as President Protempore and how long has he served in the U.S. Senate?

As of my last update, the President Pro Tempore of the U.S. Senate is Chuck Grassley, a Republican from Iowa. He has served in the Senate since 1981, making him one of the longest-serving members. Grassley has held the position of President Pro Tempore since January 2021. Please verify with up-to-date sources, as this information may change.