In terms of leadership skills, J.D. Martinez reminds me a tad of Adrian Gonzalez, another talented hitter.
In the three years before joining the Red Sox, Gonzalez had posted an OPS of .910 and an OPS+ of 151 in 452 games.
In the past three years Martinez has posted an OPS of .943 and an OPS+ of 148 in only 397 games.
Gonzalez, who joined the Red Sox when he was about 22 months younger than Martinez's current age, had a stellar first season in Boston, posting an fWAR of 6.1, a bWAR of 6.9, an OPS of .957 and and OPS+ of 155. During that 2011 season Gonzalez signed a seven-year extension through his 36th birthday with an AAV of $22 million ... the same AAV that Martinez has in his five-year contract through his 35th birthday.