Born U.B but mostly known as

Question

The goal is to come up with an answer with the help of the image below. Together with the title, they should lead to the correct answer.

Hint1

There are two different type of problems here. The portion above 'sometimes' and the portion below 'sometimes'. Together, they should guide you in the right direction.

Hint2

For the top portion, think in terms of quadrants.

Answer 1

Partial Answer

I think the ultimate answer is

Pope Gregory XIII

Who was born as

Ugo Boncompagni (initials U.B.)

The grid

If we highlight the diagonals in each quadrant as indicated by the right-angle triangles ($\sqrt{a^2 + b^2}$ indicates that we are looking the hypotenuses of each triangle) then we get the following

Reading from the left side and going clockwise, the first grid reads
BISHOP OF ROME
which is another name for the Pope. The initials grid reads
JFMAMJJASOND
which are the initials of the months of the Gregorian calendar, in order, the calendar introduced by Pope Gregory XIII

Bottom image

I can only think that the cross refers to Easter and the computus (calculation of the date of Easter). There are calendar based algorithms which change depending on whether we use the Julian or Gregorian calendar so this would hint at the symbols on the cross. Also, the "+1" might indicate the presence of a leap year (hence the meaning of "sometimes").
This part is not fully formulated which is why I've marked as Partial Answer.