In Legend of Keret we can read that:
King Keret of Hubur (or Khuburu), despite being reputed to be a son of the great god El himself.
To which El god this legend refers to?
Could be the same El as in the Bible?
According to the Wikipedia article on El, "El" was a generic name for a god, usually a supreme god. In that sense, "El" functions very much like "God" does in the English language.
ʾĒl ...is a Northwest Semitic word meaning "god" or "deity", or referring (as a proper name) to any one of multiple major Ancient Near East deities.
There are many names of God in the Bible, and many start with "El". Now, the Legend of Keret is an Ugaritic story, whereas the Wikipedia article and the Bible talk about Canaan. So, it's worth noting that
The foundations of the Bronze Age city Ugarit were divided into quarters. In the north-east quarter of the walled enclosure, the remains of three significant religious buildings were discovered, including two temples (of the gods Baal Hadad and Dagon) and a building referred to as the library or the high priest's house. Within these structures atop the acropolis numerous invaluable mythological texts were found. These texts have provided the basis for understanding of the Canaanite mythological world and religion.
[I]n the Ugaritic texts the god El is revealed to be wholly benevolent in nature, whereas Yahweh has a fierce as well as a kind side.
Indeed, looking at the original text, near the end this god El is referred to as
the Kindly One, El Benign
~ Ugaritic Myths, Epics, and Legends, p 148
I have never heard Yahweh/the Christian God (let's use "Jehovah") called "benign". He is benevolent, yes, but that's not all there is to Him. There are several more quite significant differences that further distinguish "El" and Yahweh/Jehovah, including but not limited to:
Even if the god "El" referred to in the Legend of Keret and the god that became known as Yahweh used to be the same, so to speak, by the time any of the books in the Bible were written, they were certainly different gods.
You have two questions here. I'll start with the straightforward part first.
It has been suggested that the poem was composed to glorify King Niqmad of Ugarit by giving him a deified ancester, the Keret, King of Hubur, who is the subjectof this poem. The mythological element is sufficiently prominent to justify its inclusion in an account of Canaanite mythology.
This fascinating question of is a topic under much contention among historians of the period, but I found the most compelling argument from John Day:
In the nineteenth century J. Wellhausen believed Yahweh to be the same as El, and more recently this has been particularly argued by F.M. Cross and J.C. de Moor. However, the following arguments may be brought against this. First, in the Ugaritic texts the god El is revealed to be wholly benevolent in nature, whereas Yahweh has a fierce as well as a kind side. Secondly, as T.N.D. Mettinger has rightly emphasized, the earliest evidence, such as that found in Judg. 5.4-5, associates Yahweh with the storm, which was not something with which El was connected at all. Rather, this is reminiscent of Baal. Thirdly, as for F.M. Cross's view that Yahweh was originally a part of El's cultic title, 'El who creates hosts' ('il ḏū yahwī ṣaba'ōt), this is pure speculation. The formula in question is nowhere attested, whether inside or outside the Bible. Cross's reasons for thinking that yhwh ṣb't cannot simply mean 'Lord of hosts', namely, that a proper name should not appear in the construct, is incorrect. Further hyh (hwh) is not attested in Hebrew in the hiphil ('cause to be', 'create'), though this is case in Aramaic and Syriac. Yahweh in any case more likely means 'he is' (qal) rather than 'he causes to be/creates' (hiphil): to suppose otherwise requires emendation of the Hebrew text in Exod. 3.14 ('ehyeh, 'I am'), which explains the name Yahweh. I conclude, therefore, that El and Yahweh were originally distinct deities that became amalgamated. This view was held as long ago as F.K. Movers, and has been argued since by scholars such as O. Eissfeldt and T.N.D. Mettinger.
This section in the book is very well cited and I recommend following up on his different sources; it also goes on quite fascinatingly at some length, but to do so is outside the scope of this answer.
It is necessary to make some distinctions here. While the word "el" is a generic word for a god, it is also the proper name for the head of the Canaanite pantheon, El. His origins are most directly from the Amorite god Amurru, but going further back he shared traits with Anue (An) and Ea (Enki). In Ugarit he was viewed as the creator god and, with his wife Asherah, fathered the other Canaanite gods and goddesses that we see, for example, in the Ugaritic myths including the Keret myth that you mention.
The answer to your question whether this is the same god as El in the Bible gets more complicated. The Canaanite El was originally the chief god in Palestine, where Israel later emerged. Yahweh, as the Bible itself attests several times (Deut. 33:2-3; Judg. 5:4-5; Hab. 3:3, 7; Ps. 68:8-9; Zech. 9:14), was originally from Seir (or Teman) in the Midian, which spans the east and west sides of the Araba valley in Sinai. Once Yahweh arrived in Palestine from migrants from the Midian (which echoes the stories in Exodus and Numbers), he had to compete for supremacy with the native Canaanite gods. Over time, El was merged into Yahweh, the survivor. Since this merger took place only over time, that's why we see so many references in the Hebrew Bible where Yahweh and El are intended as the same, or more accurately are retroactively explained as being the same. The issue is also confused because the different authors of the Hebrew Bible presenting different positions on this question. Thus, according to one version, the Hebrew god is announced as Yahweh (being the same as the god of Abraham which was El) to Moses at the burning bush (Exodus 3:15, by the Elohist author), which implies that Yahweh was not previously known to the Hebrews. But another author (known as the Yahwist, or J) calls God Yahweh even in the Eden story, and in Genesis 4:26 says that God was known as Yahweh almost from the beginning of humankind. This difference may reflect a situation where the traditional El remained strong in the northern kingdom of Israel, whereas the upstart god Yahweh was being promoted in Judah.
For further reference, this process of merger is discussed well in Mark Smith's book entitled The Early History of God.
As a side note, El's wife Asherah was inherited by Yahweh as a result of their merger. That too became a big issue for proponents of official Temple religion as time went on, as they tried to eliminate her.