That is just awesome! To bad you can't make him learn skills, otherwise he could improve himself even more.
I befriend my butlers and everyone that joins my families by tutoring them in skills. It's a lot easier then standing there and constantly clicking options just to carry on a conversation to work up the relationship. I also ask them to join my sims in jam sessions. Their skills actually goes up.
Most of the butlers have become such good friends with my sims, I've added them to the families. After they join, I look at their skills and see some maxed at guitar, drums etc from jamming with my sims when they were butlers.
Everyone are best friends with everyone and maxed in many skills in all my households just from tutoring each other.