Motivations. I have made several additions to that post since publishing it.
What causes motives? Why, from an early age, did I prefer reading books to playing or watching football? Why did I like Westerns (pictures of men on horses) but prefer sf (pictures of men in spacesuits)?
Let us compare the motives of Poul Anderson's characters. The "Motivations" list includes:
one individual time criminal and two groups of time criminals;
one Imperial Founder and four pretenders;
four Master Merchants of the Polesotechnic League.
I have listed two of the Master Merchants as simply wanting to get rich, also the Imperial Founder and the successful pretender as wanting to impose order. With these exceptions, all the motives differ. There are three reasons to change history and four reasons to be Terran Emperor. Two of the ET's are Wodenite converts to Terrestrial religions - but to different religions. Axor must seek evidence whereas Adzel meditates. Flandry and Desai serve the same Empire but from very different motives.
Of the motives on offer, I prefer Adzel's and Falkayn's but there is unlimited scope for readers to identify with different characters and viewpoints. Both van Rijn and Axor are Catholics - but religion can be either a vocation (Axor) or a spiritual background to a secular lifestyle (van Rijn).