Age, check. Height, check.

Temple Tower? = Challenged.
It's not suspicious if they give food and aid to the hungry and poor.
The perfect cover.

OH? Hostile takeover by the Knight's Holy Cross? Perfection.
Arthurs worship of death appeared first when he was on the brink of death itself during the ages where life extension was not a viable method, basically when it didn't exist.
He was blessed with a long life to begin with, he became 90~ years old and at the death bed he refused death, but respected it, he joined in a experimental life extension program, so he is technically living next to death at all times, he became devote in it, worshipped it like god because it is unavoidable, the perfect judge, jury and executioner, the only governing thing in this world which is just. 

He saw his life extension like a blessing from death that he would serve death untill death take him. Therefor he became an Angel of Death, in his own eyes. The political goal of the Knight's Holy Cross is to inevitably kill everything, therefor bringing them to the holy land of the afterlife, obscure? Mad? Yes. However not for a Knight. They will litterally do anything to kill everyone and everything. For different reasons that is. But the intensions that Arthur has is to become like a god figure, an all powerful.