Sul is the Korean equivalent of jutsu. It means technique (essentially).
Yudo is the Korean pronunciation of Judo, and Yusul is the Korean rendering of Jujutsu. Hapkido techniques are common to many grappling arts, including jujutsu, which Choi clamed to be trained in, though Choi's training in jujutsu and in what ryu is a matter of some debate (according to the founder, he trained in Daito Ryu Aiki Jujutsu under Takeda, though this is not universally accepted as being true). When Choi first began teaching, he called his art a number of different names, including yawara, before landing on hapkido. The first school opened up to teach the art was Seo Bok Seob's, and he called it "Hapki Yu Kwon Sul." It was later shortened to hapkido.
Whatever his background, the techniques are very similar, though hapkido traditionally does not have the ground fighting emphasis of BJJ, though some schools/organizations have incorporated BJJ into their curriculums.
As for spelling, English spelling varies depending upon the Romanization method used; sul and sool are both acceptable, though I have never seen any variations on 'yu.'
Yudo is the Korean pronunciation of Judo, and Yusul is the Korean rendering of Jujutsu. Hapkido techniques are common to many grappling arts, including jujutsu, which Choi clamed to be trained in, though Choi's training in jujutsu and in what ryu is a matter of some debate (according to the founder, he trained in Daito Ryu Aiki Jujutsu under Takeda, though this is not universally accepted as being true). When Choi first began teaching, he called his art a number of different names, including yawara, before landing on hapkido. The first school opened up to teach the art was Seo Bok Seob's, and he called it "Hapki Yu Kwon Sul." It was later shortened to hapkido.
Whatever his background, the techniques are very similar, though hapkido traditionally does not have the ground fighting emphasis of BJJ, though some schools/organizations have incorporated BJJ into their curriculums.
As for spelling, English spelling varies depending upon the Romanization method used; sul and sool are both acceptable, though I have never seen any variations on 'yu.'