Which President defined their decade the most since the 1950s

[Lincoln Republican]

1960s Nixon definitely.  He epitomized the 60s.

[Lincoln Republican]

1950's: Eisenhower
1960's: Kennedy
1980's: Reagan
1990's: Clinton
2000's: W Bush
2010's: Obama

If your signature is a slap at Trump, you know what, that is a donkey on the desk, not an elephant.

[Lincoln Republican]

1960s Nixon definitely.  He epitomized the 60s.

How so?  Nixon was President for less than one year in the 1960s.

IMO the answer would be Reagan.

Nixon was one of the most famous and influential people throughout the 60's, in or out of office.

He never quit running for President between 1960 and 1968.

[Lincoln Republican]

1960s Nixon definitely.  He epitomized the 60s.

How so?  Nixon was President for less than one year in the 1960s.

IMO the answer would be Reagan.

Nixon was one of the most famous and influential people throughout the 60's, in or out of office.

He never quit running for President between 1960 and 1968.

His run for California governor was just practice, then?

When Nixon ran for Governor in 1962, he promised not to run for President in 1964.

But he still never quit planning for his comeback to run for President in 1968.  

And I should clarify, Nixon epitomized the late 60s and early 70s.

[Lincoln Republican]

Eisenhower, Reagan and Clinton had the most public support of the listed options. You can say they defined their decades.

Nixon and Bush were very polarizing. Large swathes of the public hated them from the beginning to the end.

Nixon had quite decent approval ratings (in the 60% range) until Watergate started unfolding.

His 1968 margin of victory wasn't that great compared ti Eisenhower/Reagan/Clinton's landslide wins.

True, but there's a middle ground here.  He wasn't overwhelming popular like those three were, but he was reasonably popular with the general populace until 1973.   Also, his '68 margin was respectable (in a complex three-way race), and while it wasn't as large as those of Eisenhower/Reagan/Clinton, neither was it a squeaker like Carter's or both of Bush 43's.

And of course, his '72 margin was rather impressive.   If large swathes of the population had hated him at that time, that margin wouldn't happened, despite McGovern's weakness as a candidate.

Yes, the Nixon win in 1968 was respectable, and don't forget, his margin in the popular vote, though razor thin, translated into a very impressive win in the Electoral College, 301 to 191 to 46.