Complex sentence: He is the younger brother of the prominent rightist Tim Mudde, whom he thanks, in the preface to "The Ideology of the Extreme Right", for the respect they still have for each other despite "differences of opinion".
Split into simpler sentences: He is the younger brother of the prominent rightist Tim Mudde. In the preface to "The Ideology of the Extreme Right", he thanks his brother for the respect they still have for each other despite "differences of opinion".