Word to describe a personality which has many interests?

Solution 1:

One word is polymath.

noun
a person of wide knowledge or learning:
a Renaissance polymath

[ODO]

You could say he has an eclectic range of interests.

adjective
1 deriving ideas, style, or taste from a broad and diverse range of sources:
universities offering an eclectic mix of courses

[ODO]

Solution 2:

The word you are looking for is multipotentialite.

Multipotentiality is an educational and psychological term referring to the ability of a person, particularly one of strong intellectual or artistic curiosity, to excel in two or more different fields.

It can also refer to an individual whose interests span multiple fields or areas, rather than being strong in just one. Such traits are called multipotentialities, while "multipotentialites" has been suggested as a name for persons who wrestle with these issues. By contrast, those whose interests lie mostly within a single field are called "specialists."

While the term multipotentialite can be used interchangeably with polymath or Renaissance Person, the terms are not identical. One need not be an expert in any particular field to be a multipotentialite. Other terms used to refer to multipotentialites are scanners, slashers, and multipods, among others.

(Wikipedia)

Pertinent TED talk:

On being a multipotentialite | Anthony Rahayel | TEDxLAU

Solution 3:

Bill the engineer may be a dilettante, depending on his level of devotion to his various activities.

1 An amateur, someone who dabbles in a field out of casual interest rather than as a profession or serious interest.

2 (sometimes offensive) A person with a general but superficial interest in any art or a branch of knowledge.

In the US at least, that second definition is often assumed. Increasingly, the same negative connotation also holds for eclectic persons.

Solution 4:

I think you may need two or more English words to get a really accurate description. Of the other words here, polymath connotes wide-ranging and notable competence, and eclectic has a choosy flavor about it, things chosen very specifically for some purpose that may be best explained by looking at what was chosen.

A word I like here is lower-case 'c' 'catholic' as in 'catholic tastes'. That one implies broad-ranging interest not only in individual fields but also an interest or desire to appreciate how they all fit in the human condition.

"An energetic man of catholic tastes."