[Book 4 Hymn 26](http://www.sacred-texts.com/hin/rigveda/rv04026.htm) of the Rig Veda says begins with this verse:

> 
> aham manur abhavaṃ sūryaś cāhaṃ kakṣīvāṃ ṛṣir asmi vipraḥ |   
> 
>  ahaṃ kutsam ārjuneyaṃ ny ṝñje 'haṃ kavir uśanā paśyatā mā ||
> 
> 
> I WAS aforetime Manu, I was Sūrya: I am the sage Kakṣīvān, holy singer.
>  **Kutsa the son of Ārjuni I master.** I am the sapient Uśanā behold me.
> 
> 
> 

I'm interested in the part in bold. Who the "I" is is a complicated issue which I discuss [here](https://hinduism.stackexchange.com/q/14343/36), but suffice it to say that it's talking about the deeds of Indra. 

So my question is, who is this Kutsa and how did Indra beat him?