So solitariness vs sociality in animals is a little more complex than we usually give it credit for. For example, even in species previously thought to be largely solitary except for mating, sustained observation and tracking often shows that previously assumed to be solitary individuals actually do interact and sometimes develop lasting social relationships with conspecifics, just not at times when people are observing them. This is a particularly common finding in nocturnal animals among males who are assumed to be solitary, such as buck deer who turn out to be more social than does--just primarily at night!
That Wikipedia article you cited for 'solitary animal' is actually pretty shitty when you get down to it; the list of "solitary animals" include several generic terms for animals that include common species known to have variable social systems depending on region, such as badgers, moose, jaguars, cheetahs (in whom males, often brothers usually form lasting social relationships), red fox, and devils, who actually encounter each other quite frequently over kills and scavenging sites. (Citations are listed in this Collabedit file, because Stack Exchange is yelling at me for trying to provide actual links.)
In that context, I don't think many people have done behavioral syndrome/"animal personality" work on sociality, because it's not a particularly good thing to measure--you're really measuring something more like 'aggression threshold.' People have done work on species like social spiders where sociality varies significantly between individuals, however.