Bob is a clever and multi-talented member of Gru's vast ensemble of minions.  Unlike the other minions, he appears to be rather younger (at least in voice and appearance), and has a more innocent, boyish personality.  His eyes each have their own iris color...his right eye being green, and his left being hazel brown (a condition known as "complete heterochromia iridum".  He is also a little shorter than other minions of his body type (the short, round, heavy minions).

Despite being a boyish and apparently young minion, Bob's been around a long time.  He set out with Kevin and Stuart, some time before the minions met and came to work for Gru, in order to find some new and exciting opportunities for their people--as well as the biggest, baddest villain to serve--finding themselves briefly (and tumultuously) in the service of Scarlet Overkill, the greatest super villain of the late 1960s.  Back then, Bob was very shy and apprehensive, and carried around a teddy bear he called "Tim" (see picture below).  He also, during his youthful adventures in London, adopted a friendly sewer rat as a pet (whom he called "Pussy", perhaps thinking it was a cat).  It appears that he has come into his own since he and the other minions came to work for Gru. 

Bob should never be underestimated, however.  He actually spent one day as the king of England, having pulled the fabled sword Excalibur from the stone!

Bob with Tim, his beloved teddy bear:

(NOTE: Officially, and to the best of our knowledge, there is only one Bob in the Despicable Me franchise.  Most people will recognize him as the young minion with two different-colored eyes, as seen in the opening menu animation sequences, and closing credit sequences, of Despicable Me 2; and then as a featured minion in Minions.  However, there is a Bob listed in the credits for Despicable Me, but no minion precisely matching his description.  The closest one is a heavy-set minion who appears in the same manner as Bob does in Despicable Me 2, in the opening and closing sequences of the menu and credits, respectively.  But the eyes are one color, and he's a bit taller than the Bob who appeared in the later movies. 

We therefore have made our best guess, pending any further clarification from official sources only, of these two minions being simply different versions of the same character which evolved, between the two Despicable Me movies, into what he currently is represented to be.  Below is a screen capture of Bob as he appeared in the Despicable Me opening and closing sequences, where you can see the minor physical differences.  There is a lot of unofficial and non-canon information floating around on the internet and on various websites, purporting to be official and accurate...especially about individual minions.  None of those websites or graphics have made it clear that they have confirmed, with the copyright owners--Universal Pictures and Illumination Entertainment, that any of the material they posted is factual.  We, on the other hand, have contacted Illumination Entertainment in Los Angeles, and Illumination Mac Guff in Paris, to request clarification on this matter and others, and will correct any mistakes or erroneous information--IF THERE EVEN IS ANY HERE--as soon as they communicate with us.  Thank you for your patience and understanding in the meanwhile!)