You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "when does thanos first appear in marvel movies?" whose answer is The Avengers (2012).
Each document should contain about 30 words, and these documents should contain useful information.

Query: Thanos first appearance in Marvel movies
Useful Output:

Doc 1: In Marvel Comics, Thanos was first introduced in 1973's The Invincible Iron Man #55, and has since appeared in five decades of publications
Doc 2: Avengers (2012) Mid Credit scene.Thanos first appearance.Mini Movies. · Comments28.
Doc 3: Here's every Thanos appearance: 1. The Avengers 2. Guardians of the Galaxy 3. Avengers: Age of Ultron 4. Avengers Infinity War and Endgame 5
Doc 4: 2014 Thanos First Appearance // "We Will Not Fail You Father" | Avengers: Endgame [Blu-Ray HD] Property of Marvel Studios.
Doc 5: Thanos (UK: /ˈθænɒs/, US: /-oʊs/) is a fictional comic book supervillain appearing in publications by the American publisher Marvel Comics.