Who was the swimmer in the Barcelona Olympics whose country had never been in the Olympics before?

Answer 1

Here are a list of medalists in swimming at the 1992 Olympics:

http://en.wikipedia.org/wiki/Swimming_at_the_1992_Summer_Olympics

The notable thing about the participants at the 1992 games is that with the breakup of the Soviet Union, a lot of participants represented "Unified Team", which consisted of most of the former Soviet states competing together. That could be considered several "new countries", since the countries that made up the Unified Team didn't exist at the previous Olympics in 1988 and had all competed together as the USSR. 3 of the individual medalists at swimming in 1992 and 2 teams were representing the Unified Team, with most of them being Russian and at least one being Ukrainian, and it could be argued that all of the Unified Team participants were representing new Olympic countries.

The new countries that participated independently for the first time at the 1992 Olympics were former Soviet states Estonia, Latvia and Lithuania (who weren't part of the Unified Team) and former Yugoslav states Croatia, Serbia and Bosnia-Herzegovina.

I've got a reference here to Estonia being part of the men's 4x100 relay, meaning Estonia fielded at least 4 swimmers:

http://en.wikipedia.org/wiki/Swimming_at_the_1992_Summer_Olympics_-_Men%27s_4_x_100_metre_medley_relay

So, I'm sure you have a single athlete in mind, but with the number of new countries competing in the 1992 games and with most of them fielding a swimmer in some form, there are multiple answers to this question.