Unlike means different from the thing named. Not the same, and the sentence is about to say how.
It is a preposition, so it takes an object directly: unlike his brother, unlike anything I had seen. It also carries a note of judgement about character, since saying that behaviour is unlike somebody means it is out of character for them, and that is a very common British usage. Take care with the adjective unlikely, which means improbable and is a different word entirely.
Unlike is exactly as old as it looks. Old English unġelīċ, un plus like, meant different or dissimilar, and the word has held its shape for a thousand years.
Proto-Germanic
*ungalīkaz
Old English
unlīċ
Middle English
unlic
English, today
unlike
Built from
From Middle English unlic, unlich, from Old English unlīċ, unġelīċ (“unlike, different, dissimilar, diverse”), from Proto-Germanic ungalīkaz. by surface analysis, un- + like. Cognate with Dutch ongelijk, German ungleich, Old Norse úlíkr (see there for North Germanic descendants).
Etymology from Wiktionary, CC BY-SA