Martin defected from Cuba in 2010, and has been linked with the Rangers for the past couple of weeks. The scouting reports on Martin have varied, but the consensus seems to be that he's got good speed and at least an average arm (some reports saying better than average), with a little bit of power, good plate discipline and questions about his hit tool.
Kevin Goldstein tweeted earlier this week that Martin isn't as good as Jacoby Ellsbury, the Boston Red Sox centerfielder. The questions that Martin will have to answer are whether he has the range to be a quality defender in centerfield, and how much he'll hit.
Martin seems unlikely to contribute this year, and even 2012 might be pushing it, but either he or Engel Beltre should be poised to move into centerfield for the 2013 season, if Julio Borbon hasn't nailed down the position permanently by then.
UPDATE -- Ramon Aguero has been designated for assignment to make room for Martin on the 40 man roster.
UPDATE II -- For folks who don't remember, the Rangers claimed Aguero on waivers on April 8 from Pittsburgh.