I think Tom is the cleverer of the two boys who is the first to solve the problem.
老师,请问这里who指代的谁?根据后面的谓语用的is,那说明指代的应该是Tom,那who的前面是不是应该加逗号?
你的看法是正确的。即who的前面应该加逗号,引导一个非限制性定语从句。