Who decides what kind of token reward a miner gets for mining a block?

Question

Preamble:

• To my understanding, a Bitcoin miner creates a new block, put some necessary information in it incl. some transactions from other participants and one transaction which sends 25 Bitcoin to his own address as 'Reward' in case he manage to actually 'mine' the block by solving a cryptologic riddle.

My Question:

• How does it behave on ethereum?

  On the ethereum blockchain new blocks will be also mined. But who decides which reward the miner gets in case he successfully manage to solve the riddle? Is it like on BTC that the miner itself just adds (one) transaction with a specific amount of a specific Token?

Answer 1

... which sends 25 Bitcoin to his own address as 'Reward'...

The reward hasn't been 25 BTC since July 2017, when it halved to 12.5.

But who decides which reward the miner gets in case he successfully manage to solve the riddle?

The title of your question implies that by "which reward" you mean the type of reward, rather than quantity. Standard block rewards are in ETH, not ERC-20 (or any other) tokens.

The current standard block reward is 3 ETH, which will reduce to 2 ETH on the 16th January 2019, as part of the Constantinople hard fork. See EIP-1234.

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However, it's worth considering transaction fees - which are also paid to the miner - as well as the main block reward.

It's possible at some point that transaction fees will be able to be paid in tokens. See the following:

• ERC865: Pay transfers in tokens instead of gas, in one transaction
• Paying a transaction fee with an ERC20 token

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Is it like on BTC that the miner itself just adds (one) transaction with a specific amount of a specific Token?

The protocol adds the mining reward (i.e. block reward, transaction fees, uncle fees) to the balance of the miner's coinbase address.